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This is to certify that the
dissertation entitled

DISPERSAL ECOLOGY AND CONTROL OF THE INVASIVE
LAND SNAIL CEPAEA NEMORALIS (L. 1758), FROM
INGHAM COUNTY, MICHIGAN

presented by

MERRITT GALE GILLILLAND III

has been accepted towards fulfillment
of the requirements for the

 

 

 

 

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DISPERSAL ECOLOGY AND CONTROL OF THE INVASIVE LAND SNAIL
CEPAEA NEMORALIS (L. 1758), FROM INGHAM COUNTY, MICHIGAN
By

Merritt Gale Gillilland III

A DISSERTATION

Submitted to
Michigan State University
in partial fulfillment of the requirements
for the degree of

DOCTOR OF PHILOSOPHY

Department of Zoology

Program in Ecology, Evolutionary Biology, and Behavior
2006

ABSTRACT

DISPERSAL ECOLOGY AND CONTROL OF THE INVASIVE LAND SNAIL
CEPAEA NEMORALIS (L. 1758), FROM INGHAM COUNTY, MICHIGAN

By
Merritt Gale Gillilland III
Cepaea nemoralis is an exotic and invasive species of land snail in North
America. To understand how this species could potentially spread it was necessary to
determine its short-distance dispersal capabilities. Harmonic radar was used to track the
daily and weekly dispersal of this land snail species in two distinct habitat types from
2003 — 2005. The first habitat type was woodland with both biotic and abiotic conditions
suitable for this species. The second habitat was grassland and was not considered a
suitable type for this species. Cepaea nemoralis dispersed further distances in the
woodland habitat (2.1 m/day) than in the grassland habitat (0.39 m/day). Snail dispersal
was closely related to the abiotic (temperature and relative humidity) conditions of the
environment. The woodland habitat was significantly cooler and more humid than the
grassland habitat. Snail activity was greatest when the temperature ranged from between
19 — 20 °C and the relative humidity was above 80%. This population of C. nemoralis
was comprised mostly of 5 banded individuals and was dominated (85.1%) by juveniles.
A commercially manufactured molluscicide was evaluated for its effectiveness at
controlling C. nemoralis. It was determined that snail mortality was significantly higher
in areas treated with the molluscicide than in areas treated with no molluscicide or sham
molluscicide. The snail mortality also increased during successive treatments with the
molluscicide. The efficacy of using harmonic radar to track the daily and weekly

dispersal of C. nemoralis was evaluated. Harmonic radar is a useful tool that can be used

to determine the dispersal of land snails. In this study the with daily tracking success
rates ranged from 74% to 100% and weekly tracking success rates ranged from 40% to

52%.

DEDICATION

I would like to dedicate this dissertation to my wife, Carolyn and my son, Brennan. You
both make life so very interesting.

ACKNOWLEDGMENTS

To start, I would like to thank my advisor, Dr. James W. Atkinson, for all of his
help and continued guidance over the years and for the intriguing and long discussions
about science, philosophy, politics and sports. I am in debt to my guidance committee,
Dr. Doug Landis, Dr. Jim Smith and Dr. Richard Snider for their constructive criticism
throughout this project and for their help in the design and execution of the experiment.
Special thanks are owed to the private landowners, Brad and Anna Stockwell, for
allowing me access to their land, and most importantly, the snails for 3 years. I want to
also acknowledge Dr. Doug Landis and the Invasive Species Ecology and Biological
Control Lab for allowing me to use the RECCO Detector and thermohygrometer in the
field. I would also like to graciously thank those who helped me in the field on one or
more occasions, my father, Mr. M. Gale Gillilland Jr., Ms. Bridget Kruger, Dr. James
Atkinson, Dr. Jim Smith, and Ms. Alicia Bray. Soil chemistry analyses were paid for by

the MSU Invasive Species Initiative.

TABLE OF CONTENTS

LIST OF TABLES ........................................................................... viii
LIST OF FIGURES .......................................................................... ix
CHAPTER 1: INVASIVE SPECIES ..................................................... 1
Introduction ................................................................................. 1
Invasive Species: Examples of Selected Taxa ...................................... 1
Invasive Terrestrial Gastropods ...................................................... 4
CHAPTER 2: NATURAL HISTORY OF CEPAEA NEMORALIS ............... 12
Description ................................................................................. 12
Reproduction ................................................................................ 1 3
Habitat, Diet and Food Preference ....................................................... 13
Shell Polymorphism ........................................................................ 14
CHAPTER 3: USING HARMONIC RADAR TO TRACK CEPAEA
NEMORALIS .................................................................................. 18
Introduction ................................................................................. 1 8
Materials and Methods .................................................................... 19
Harmonic Radar ........................................................................ 20
Results ....................................................................................... 21
The Pilot Study 2003 .................................................................. 21
2004 ...................................................................................... 22
2005 ...................................................................................... 22
Discussion ................................................................................... 24

CHAPTER 4: DISPERSAL, POPULATION DENSITY, AND

DISTRIBUTION OF CEPAEA NEMORALIS .......................................... 27
Introduction ................................................................................. 27
Materials and Methods ..................................................................... 30

The Study Site and Habitat ............................................................ 30
Dispersal ................................................................................. 32
Population Density ..................................................................... 34
Soil Chemistry .......................................................................... 34
Distribution .............................................................................. 35
Statistics ................................................................................. 35
Results ....................................................................................... 36
Dispersal ................................................................................. 36
2003 Pilot Study ..................................................................... 36

14 Day Temperature, Relative Humidity and Dispersal in the SC and SF
2004 ................................................................................... 37

Weekly Temperature, Relative Humidity and Dispersal in the SC and SF
2004 ................................................................................... 38

vi

TABLE OF CONTENTS (CONT’D)

14 Day Temperature, Relative Humidity and Dispersal in the SC and SF

2005 ................................................................................... 39
Population Density and Demographics .............................................. 41
Distribution .............................................................................. 41

Discussion ................................................................................... 42
CHAPTER 5: CONTROL OF CEPAEA NEMORALIS .............................. 94
Introduction ................................................................................. 94
Control of Land Gastropods ........................................................... 94
Iron Phosphate ........................................................................... 97
Materials and Methods ..................................................................... 97
Study Design ............................................................................ 98
Symptoms of Intoxication ............................................................. 99
Statistics ................................................................................. 99
Results ....................................................................................... 100
Post-Application (One Week) ......................................................... 100
Post-Application (Two Weeks) ....................................................... 100
Discussion ................................................................................... 101

CHAPTER 6: GENERAL CONCLUSIONS AND RECOMMENDATIONS... 107

General Conclusions ....................................................................... 107

Recommendations .......................................................................... 1 14
APPENDIX A ................................................................................. 117
APPENDIX B ................................................................................. 120
APPENDIX C ................................................................................. 122
APPENDIX D ................................................................................. 124
APPENDIX E ................................................................................. 126
APPENDIX F .................................................................................. 128
APPENDIX G ................................................................................. 131
APPENDIX H ................................................................................. 138
APPENDIX 1 .................................................................................. 159
LITERATURE CITED ...................................................................... 161

vii

LIST OF TABLES
CHAPTER 4

Table 4.1. The mean (i SE) daily daytime, nighttime, and time of collection
temperature (°C) for Snail Central and South Field 2004 taken at the height of 10
cm using a HOBO datalogger ................................................................

Table 4.2. The mean (1 SE) daily daytime, nighttime, and time of collection
relative humidity (%) for Snail Central and South Field 2004 taken at the height of
10 cm using a HOBO datalogger ............................................................

Table 4.3. The mean (3: SE) weekly daytime, nighttime, and time of collection
temperature (°C) for Snail Central and South Field 2004 taken at the height of 10
cm using a HOBO datalogger ................................................................

Table 4.4. The mean (i SE) weekly daytime, nighttime, and time of collection

relative humidity (%) for Snail Central and South Field 2004 taken at the height of
10 cm using a HOBO datalogger ............................................................

Table 4.5. The mean (t SE) daily daytime, nighttime, and time of collection
temperature (°C) for Snail Central and South Field 2005 taken at the height of 10
cm using a HOBO datalogger ................................................................

Table 4.6. The mean (i SE) daily daytime, nighttime, and time of collection
relative humidity (%) for Snail Central and South Field 2005 taken at the height of
10 cm using a HOBO datalogger ............................................................

Table 4.7. The mean (i SE) daily and weekly dispersal (meter) of C. nemoralis
from SC in 2003 and from SC and SF in 2004 and 2005 .................................

Table 4.8. Soil nutrients and pH from the SC and SF 2005 ..............................
CHAPTER 5

Table 5.1. The mean :t SE of live and dead C. nemoralis found before treatment
and during week one and week two post-application, the total number of adults
and juveniles found in each treatment group and the percent dead C. nemoralis

after treatment for SC in 2005 ................................................................

Table 5.2. The mean :t SE temperature (°C) relative humidity (%) in each of the 5
blocks per week of treatment in SC 2005 ...................................................

viii

54

55

56

57

58

59

60

61

104

105

LIST OF FIGURES

CHAPTER 4

Figure 4.1. Map outlining the 5 distinct patches (snail central, blue spruce, south

field, north field, and homestead) within the study area in Ingham County,

Michigan ........................................................................................ 62

Figure 4.2. Air and soil temperature (Celsius) taken over a 14 day period
(5/ 18/2003 - 5/31/2003) in the SC ........................................................... 63

Figure 4.3. The mean daily dispersal (i 1 SE) of C. nemoralis from SC in 2003
and the SC and SF in 2004 and 2005 ........................................................ 64

Figure 4.4. Weekly air and soil temperature (Celsius) taken from 6/11/2003 -
9/26/2003 in the SC ............................................................................ 65

Figure 4.5. The mean weekly dispersal (i: 1 SE) of C. nemoralis from SC in 2003
and the SC and SF in 2004 .................................................................... 66

Figure 4.6. Temperature (Celsius) taken at ground level over a 14 day period
(6/05/2004 - 6/18/2004) in the SC and SF .................................................. 67

Figure 4.7. Relative Humidity (%) taken at ground level over a 14 day period
(6/05/2004 - 6/ 18/2004) in the SC and SF .................................................. 68

Figure 4.8. Regression analysis of C. nemoralis daily dispersal and relative
humidity (%) from SF in 2004 ............................................................... 69

Figure 4.9. Regression analysis of C. nemoralis daily dispersal and temperature
(celsius) from SF in 2004 ..................................................................... 70

Figure 4.10. Regression analysis of C. nemoralis daily dispersal and relative
humidity (%) from SC in 2004 ............................................................... 71

Figure 4.11. Regression analysis of C. nemoralis daily dispersal and temperature
(celsius) from SC in 2004 ..................................................................... 72

Figure 4.12. Weekly temperature (Celsius) taken at ground level from 6/25/2004 -
9/15/2004 in the SC and SF .................................................................. 73

Figure 4.13. Weekly relative humidity (%) taken at ground level from 6/25/2004 -
9/15/2004 in the SC and SF .................................................................. 74

Figure 4.14. Temperature (Celsius) taken at ground level over a 14 day period
(6/08/2005 - 6/21/2005) in the SC and SF .................................................. 75

LIST or FIGURES (CONT’D)

Figure 4.15. Relative Humidity (%) taken at ground level over a 14 day period
(6/08/2005 - 6/21/2005) in the SC and SF .................................................. 76

Figure 4.16. Regression analysis of C. nemoralis daily dispersal and relative
humidity (%) from SC in 2005 ............................................................... 77

Figure 4.17. Regression analysis of C. nemoralis daily dispersal and temperature
(Celsius) from SC in 2005 .................................................................... 78

Figure 4.18. Regression analysis of C. nemoralis daily dispersal and relative
humidity (%) from SF in 2005 ............................................................... 79

Figure 4.19. Regression analysis of C. nemoralis daily dispersal and temperature
(celsius) from SF in 2005 ..................................................................... 80

Figure 4.20. Specific patch and population density (snails/m2) of C. nemoralis in
2003 .............................................................................................. 81

Figure 4.21. The number of bands present (percentage of population) in C.
nemoralis from the SC in 2005 ............................................................... 82

Figure 4.22. The percentage of juvenile and adult C. nemoralis from the SC in
2005 .............................................................................................. 83

Figure 4.23. The distribution of C. nemoralis by size class (adult, large juvenile,
medium juvenile and small juvenile) from the SC in 2003 .............................. 84

Figure 4.24. The distribution of C. nemoralis by size class (adult, large juvenile,
medium juvenile and small juvenile) from the SC in 2005 .............................. 85

Figure 4.25. The mean daily dispersal (meters) of C. nemoralis and relative
humidity (%) from SC in 2004 ............................................................... 86

Figure 4.26. The mean daily dispersal (meters) of C. nemoralis and temperature
(celsius) from SC in 2004 ..................................................................... 87

Figure 4.27. The mean daily dispersal (meters) of C. nemoralis and relative
humidity (%) from SF in 2004 ............................................................... 88

Figure 4.28. The mean daily dispersal (meters) of C. nemoralis and temperature
(celsius) from SF in 2004 ..................................................................... 89

Figure 4.29. The mean daily dispersal (meters) of C. nemoralis and relative
humidity (%) from the SC in 2005 .......................................................... 90

LIST OF FIGURES (CONT’D)

Figure 4.30. The mean daily dispersal (meters) of C. nemoralis and temperature

(celsius) from the SC in 2005 ................................................................ 91
Figure 4.31. The mean daily dispersal (meters) of C. nemoralis and relative

humidity (%) from SF in 2005 ............................................................... 92
Figure 4.32. The mean daily dispersal (meters) of C. nemoralis and temperature

(celsius) from SF in 2005 ..................................................................... 93
CHAPTER 5

Figure 5.1. The mean (i SE) number of live snails found per block before
application of molluscicide ................................................................... 106

xi

CHAPTER 1: INVASIVE SPECIES
INTRODUCTION
Invasive Species: Examples of Selected Taxa

It has been suggested that exotic species are now the number one threat to
biodiversity (Cohen, 2002). Once established in a new area these invading organisms can
devour native species, compete with native species, alter existing habitats, hybridize with
native species, and possibly infect them (Simberloff et al., 2005). Many factors are
important for an invading organism to possess in order for that organism to successfully
establish in a new habitat: (1) ability to readily adapt to a new or changing environment;
(2) to out-compete native species within the same niche; (3) to have a wide tolerance to
biotic and abiotic factors; (4) to have very few predators in the newly colonized area; (5)
to be a generalist; (6) to grow quickly with high reproductive rates; (7) have long-
distance and short-distance dispersal of offspring; and (8) to live at high population
densities.

Examples of the introduction, establishment, Spread, ecological damage, and
economic cost an invading organism can have are numerous. The zebra mussel,
Dreissena polymorpha (Pallas, 1771), was first detected in the Great Lakes in 1988
(Garton et al., 1993). It is believed that this invader was accidentally introduced via
release of ballast water from ships used for maritime commerce. Infested ships came
from parts of Europe where D. polymorpha is native. This species is now being spread
from one inland lake to another in the US. primarily through recreational boating. It is
estimated that D. polymorpha control costs the US. $100 million annually. This Species

can plug water intake and discharge pipes of water systems used by industries and

municipalities. Industries and municipalities that use the Great Lakes as a water supply
pay ~$360,000/year to control this invading aquatic mollusc (Glassner-Shwayder, 1998).
It has been estimated that between the years 1989-1994 D. polymorpha cost Great Lake
companies and municipalities over $120 million. Further, the nationwide cost to US.
industries is over $1 billion annually.

The ecological impact of D. polymorpha is even greater than the economic
impact. In Europe it was reported that these mussels can live at densities of 10,000/m2
(Garton et al., 1993). Dreissena polymorpha also has free-swimming planktonic larva
which provides for long- and short-distance dispersal in the aquatic environment
(Ackerman et al., 1994). An individual female can release as many as 300,000 eggs in
one season (Garton et al., 1993). In Lake Erie D. polymorpha was responsible for
increasing water clarity by decreasing phytoplankton numbers found in the water column,
detrimentally altering pelagic and benthic food webs (Garton et al., 1993). Native North
American unionid clams are also negatively affected by D. polymorpha. They will attach
to any hard surface, including native unionid shells.

Purple loosestrife, Lythrum salicaria (L.), was introduced to the east coast over
200 years ago and since has spread throughout most of the US. It has been reported in
40 of the 48 continental states (Glassner-Shwayder, 1998). It has had significant
economic impacts costing the US. $45 million annually (Pimentel et al., 2000). This
plant is a good example of a species that can dominate communities. Lythrum salicaria
will out-compete native plants, especially cattail, Typha spp., forming a monoculture. A
mature plant can produce over 2.7 million seeds annually and remain viable for up to 5

years (WSDE, 2004). Seeds are small, light and disperse via wind, water, and animals

(e.g. birds); it can also spread vegetatively via a spreading rootstock (WSDE, 2004). This
plant is a threat to biodiversity; not only to other plant species, but to those organisms
that use the native plant species as resources.

More recent introductions into the US. include the emerald ash borer, A grilus
planipenm‘s Fairmaire 1888, which was discovered in Michigan in 2002 (MacFarlane and
Meyer, 2005). This destructive insect has killed millions of ash trees, F raxinus Sp. The
green macroalga, Caulerpa spp. “killer alga” is currently becoming established in the
US. This species is widely bought and sold by the aquarium trade (Walters et al., 2006).
Highly invasive, its sale via the intemet is mostly unregulated. The northern snakehead
fish, Channa argus (Cantor, 1842), was first reported in 2003 from Maryland (Simberloff
et al., 2005). Brought to this country via ethnic markets to be sold as food, it has since
spread into American waterways (Odenkirk and Owens, 2005). It is feared that the
species will damage native fisheries and have major economic and ecological impacts.

At least 20 different mammal species have been introduced into the US.
(Pimentel et al., 2000). Many of these species (European rat, Rattus rattus (Linnaeus,
175 8), and the Asiatic rat, R. norvegicus (Berkenhout, 1769)) have established
themselves as terrible pest species throughout much of the US. The Indian mongoose,
Herpestes auropunctatus (Hodgson, 1836), was introduced to Hawaii as a biological
control for rats. Since its introduction it has eaten many of the native ground-nesting
birds (Pimentel etal., 2000). At least 53 species of reptiles and amphibians have been
introduced into the Continental US. and its territories. Among them is the brown tree
snake, Boiga irregularis (Merrem, 1801 ), of Australia which was transported to the

island of Guam via military airplanes during World War II (Pimentel et al., 2000). This

snake has now consumed much of the islands native mammals, birds and lizards.

The examples mentioned above are but a few of the tens of thousands of exotic
animals and plants introduced into the US Pimentel et al. (2000) estimated that 50,000
new animal and plant Species have been introduced at a cost of $137 billion per year to
manage, control, and eradicate. These numbers are expected to continue to increase with
no foreseeable decrease. Human activity is the primary cause of these new animal and
plant introductions around the world. Global economy and world trade are major
influences that promote spread of invasive species. A much more recent world
phenomenon (e-commerce and the intemet) is also playing a major role in spreading
exotic species with the simple click of a computer mouse (Walters et al., 2005). Much of
the e-commerce trading in exotic species goes on unregulated and invasive Species move
quietly around the US. and the world via the US. Postal service and other private
shipping companies (Walters et al, 2005). Detrimental human activity that can also
promote spread of exotic animals includes modification of natural landscapes. Habitat
fragmentation can produce an ideal situation for invasives by creating new habitats that
can benefit spreading of biological invaders (Harris and Silva-Lopez, 1992).

Invasive Terrestrial Gastropods

Invading gastropods have many routes to gain entry into a new area. The
introductions can be deliberate or accidental and the majority of times the introduction
has been anthropogenic. Cowie (2005) reviewed several modes that can lead to
introduction of gastropods and lists six routes that can be used for deliberate introduction
of land and aquatic gastropods to new areas: (1) aquarium industry to be sold as pets, (2)

food industry to consume as a food source, (3) medicinal purposes, (4) as a biological

control for other snail species, (5) for aesthetics and their remarkable appearances, and
(6) for biological research and experimentation. Cowie (2005) also lists many routes for
the accidental introduction of land gastropods to new areas, as hitchhiker’s on
agricultural products, horticultural products, commercial and domestic Shipments,
military shipments, soil, aquarium industry, aquaculture, Ships and boats, and airplanes.
It is not known what effect many of these land gastropods have had once they are
introduced to new areas because they frequently go unnoticed for great lengths of time,
there are not enough trained malacologists studying them and land gastropods can be
misidentified leading to confusion which retards any control strategies that could be
implemented (Robinson and Slapcinsky, 2005). Preventing introduction is also crucial in
stopping invaders from becoming established. Cowie (2005) called for better quarantine
strategies, pre-entry regulations and screening, and establishing a rapid response to
eradicate new populations of invading land snails as a way to prevent establishment and
spread of an invader.

Over 80 species of land gastropods have been introduced to the continental US.
and Canada including seven recent introductions of serious land gastropod pests
(Robinson and Slapcinsky, 2005). Seven recently introduced non-native snails by Site of
introduction are: (1) Beckianum beckianum Pfeiffer, 1846 (Broward County, Florida); (2)
Paropeas achatinaceum Pfeiffer, 1846 (Palm Beach County, Florida); (3) Bulimulus
tenuissimus pueIlaris (Orbigny, 1835) (New Hanover County, North Carolina); (4)
Ovachlamysfulgens (Gude, 1900) (Broward County, Florida); (5) Monacha cartusiana
(Muller, 1774) (Newcastle County, Delaware); (6) Monacha syriaca (Ehrenberg, 1831)

(Brimswick County, North Carolina); and (7) Xerolenta obvia (Menke, 1828) (Detroit,

Michigan). These species came from Southern Europe, Central and South America and
were most likely brought in accidentally by shipping containers (Robinson and
Slapcinsky, 2005).

Some introduced gastropods can have impact beyond the environment, posing
serious health risks to humans as the intermediate hosts to infectious agents. The giant
Afi'ican land snail, Achatinafulica (Bowdich, 1822), is native to Kenya and since the 18th
Century it has spread around the globe (Smith, 2005). This species is an intermediate
host to the rat lungworm, Angiostrongylus cantonensis (Chen, 1935), which can cause a
serious disease (eosinophilic meningoencephalitis) in humans if raw and undercooked
snails are eaten (Waugh et al., 2005). Achatinafulica also carries the bacterium,
Aeromonas hydrophila (Chester, 1901 ), which can cause osteomyelitis, septic arthritis,
tonsillitis and meningitis in humans (Smith, 2005). Achatinafulica was deliberately
introduced into Florida in 1966 by a young boy returning from Hawaii where it was also
an invader. The Florida population was eradicated in 1975, but at a cost of $700,000 and
seven years of eradication work (Smith, 2005).

Aside from being an intermediate host for infectious agents A. fulica is also a
serious pest species. It has been documented that A. fidica will eat over 500 different
plant Species (USDA-APHIS, 2005). Achatinafulica was introduced to Hawaii in 1936,
becoming established, and consuming indigenous plant species (Cowie, 2005). In an
attempt to control and eradicate A. fidica in Hawaii many carnivorous land snails were
introduced to eat this snail species. Of the carnivores introduced Euglandina rosea
(Ferussac, 1821) became established and is now consuming the native and threatened

Hawaiian tree snails, Achatinella spp., instead of the target organism, A. fulica (Hadfield

etaL,1993)

Management of introduced gastropods includes eradication and control strategies
(Barker, 2002; and Cowie, 2005). If an introduced exotic species is detected early
enough, it may be possible to eradicate them before they become established. For
example, a population of Achatina fulica was discovered in California in the 1940’s and
because it had not yet established as population, it was successfully eradicated from that
area (USDA-APHIS, 2005).

Achatinafulica has been reported in 9 states throughout the Midwest and eastern
United States, but no populations have become established and all introductions have
been eradicated (U SDA-APHIS, 2005). Achatinafulica was sold in the US. as a pet and
for biological research. The USDA began controlling A. fulica in 2004, and the last
cohort was found and removed from Michigan by the USDA on September 28, 2004
(USDA-APHIS, 2005). It is now illegal to own or possess A. fidica in the US. without a
government issued permit. The story of A . fulica demonstrates what can go wrong when
a new invasive species iS introduced and little is known about its natural history.

It is not currently known what impact the exotic invader C epaea nemoralis
(Linnaeus, 1758), is having in North America because no research has yet been
performed. It has been ignored as a pest by the USDA-PPQ and is considered established
in the US. (Sullivan et al., 2004). Dr. W. G. Binney, an English malacologist, first
introduced C. nemoralis into the US. in 1857, at his home in Burlington, New Jersey
(Reed, 1964). Dr. Binney imported the snails from England to release in his private
garden for reasons that were purely aesthetic. It is interesting to note that Binney himself

declared “The whole town is full of them now”, only eight years afier their introduction

(Reed, 1964). Twenty-two years later a second population of C. nemoralis was found in
Lexington, Virginia, and was reported by Pilsbry in 1889 (Reed, 1964). This second
population of C epaea was introduced from Italy for unknown reasons. Since its
introduction it has spread throughout the United States and Canada.

The most complete list describing the occurrence of C. nemoralis in North
America was complied by Reed (1964), which reported the snail in 17 states (California,
Colorado, Indiana, Kentucky, Maryland, Massachusetts, Missouri, New Jersey, New
Hampshire, New York, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee,
Virginia, and Wisconsin) and from Ontario and Quebec, Canada. As of 1964, C.
nemoralis had not been reported in Michigan, it is not known when this species was first
reported in this state. To date, C. nemoralis, in Michigan, has only been officially
reported from Ingham, Lapeer and Sanilac Counties (MSU-1PM, 2001). Anecdotal
reports have also placed this organism in Presque Isle, Gratiot, Oakland and Wayne
Counties Michigan.

In Germany C. nemoralis has been reported as a pest species from agricultural
areas and grasslands (i.e. beets, spring grain, clover, and lucem), gardens and
greenhouses (i.e. kidney bean, chicory, cucumber, pumpkin, and spinach), viticultures
and ornamentals (i.e. black currant, apple, pear, grapevine, monks hood, and jimson
weed), and by forest managers on trees (i.e. beech, alder, larch, and poplar) (Godan,
1983). Cepaea nemoralis has been reported as a pest in raspberries and black currant in
England (Godan, 1983). Other countries that recognize C. nemoralis as a pest species are
Belgium, Canada, France, Portugal, Russia, Spain, Sweden, and the United States

(Godan, 1983, USDA, 1959).

Martinson (1999), reported C. nemoralis as a vineyard pest in Ontario, Canada. It
was found during this study that the snail fed superficially upon grapevines and seemed
to use them as a daytime roost. The snail became a problem when it was picked
accidentally with grapes and fouled the product being produced (wine). Martinson also
indicated that California citrus producers easily control C. nemoralis by girdling trees
with copper foil, which creates a barrier the snail seems unable to traverse. In Michigan,
C. nemoralis has been reported as a pest species in a private flower/vegetable garden and
hay field in Lapeer and Sanilac Counties (MSU-1PM, 2001).

Ehrlich (1986) listed eight characteristics which are important for invasion of a
novel habitat by a terrestrial, exotic species, and they are: (1) numerous and abundant in
original range; (2) polyphagous diet; (3) short generation times; (4) high degree of
genetic variation; (5) females are able to colonize after fertilization; (6) physically larger
than other related species; (7) human association; and (8) wide tolerance for different
environments. Cepaea nemoralis is (1) numerous and abundant in Western Europe; (2)
has a polyphagous diet; (3) fertile individuals (snails are hermaphroditic) are able to
colonize new areas; (4) has a high fecundity and can mate multiple times during the
spring and summer seasons; (5) has a high degree of genetic variation; (6) is larger than
most other snail species; and (7) is associated with humans. Ehrlich (1986) suggested
that a species possessing one or more of these characteristics would be a candidate to
become a ‘good’ biological invader. Cepaea nemoralis possesses seven of these eight
characteristics making it a good candidate for an invasive species. This snail species also
has a propensity to survive at high population densities. In summary, all of these natural

history traits make C. nemoralis an ideal invasive Species and it should be subjected to

further investigation here in Michigan and elsewhere.

Terrestrial gastropods face challenges to dispersal that other animal taxa are often
better at overcoming. These challenges are closely tied to the physical conditions of the
environment (temperature and humidity). Because of this, very little attention is often
paid to their short-distance dispersal. Terrestrial gastropods are thought to have poor
dispersal capabilities because they are stereotyped as being very slow and not capable of
traversing great distances on their own. In contrast, animals that are considered to have
good dispersal capabilities are mammals, birds, reptiles, amphibians, fish, insects, and
plants. Animals that can run, walk, hop, crawl, fly, swim or release seeds to be
transported by wind or water they are usually considered as having greater dispersal
capabilities than an animal that glides over a trail of mucus. Human mediated long-
distance dispersal of gastropods is very important for their dispersal.

Shigesada and Kawasaki (2002) suggested that it is imperative to collect detailed
statistical data on dispersal and natural history of the invader to understand how it will
spread. No attempt has ever been made to quantify the spread of or dispersal capabilities
of C. nemoralis in North America. The most likely means of C. nemoralis long-distance
dispersal is anthropogenic and passive making its association with humans a very
important characteristic. It is vital to understand how this Species will disperse naturally.
Since it is very likely that the presence of C. nemoralis will remain unnoticed in many
areas within the US. it is important to have data on its short-distance dispersal so when
populations are found managers can determine how it will spread. Being ignored could
allow C. nemoralis to slowly spread over large areas becoming further established and

more difficult to eradicate. If managers remain complacent towards C. nemoralis this

species could become the proverbial time-bomb and explode as a pest species.

Once invading gastropods become established they can have serious impact on
the environment, human health, and cost millions to control and manage. While there are
no current dollar estimates for the impact these invading gastropods have had, the overall
impact of non-native Species has been staggering. This species should still be treated
more seriously as an invasive Species and its spread should be controlled through

eradication programs.

ll

CHAPTER 2: NATURAL HISTORY OF CEPAEA NEMORALIS

INTRODUCTION

The banded wood snail, Cepaea nemoralis, is a pulmonate land snail and can be
found in a wide range of terrestrial habitats. It currently has a Palaearctic and Nearctic
distribution and native to Western Europe. Cepaea nemoralis was introduced to North
America in 1857 (Reed, 1964). This species is highly polymorphic and perhaps best
known from field studies of natural selection by Arthur Cain and Philip Sheppard, at
Oxford University, in the 1950’s (Cain and Sheppard, 1954). Cain and Sheppard
attempted to explain the selective force(s) responsible for maintaining a balanced
polymorphism of banded and non-banded shells within European populations of C.
nemoralis. Cepaea nemoralis has also been regarded as one of the most damaging pest
land snail species known. In Europe, C. nemoralis is responsible for causing much
damage to the plants commonly associated with greenhouses, gardens, viticultures,
ornarnentals, grasslands, forests, and in agriculture (Godan, 1983). In North America it
has been reported as a pest from the vineyards of Ontario, Canada and Upstate New
York, and from the citrus producers of California.

Description

Cepaea nemoralis is placed in the Family Helicidae, a group of medium to large
size snails. The shell of C. nemoralis is known to have several different background
colors (yellow, red, pink and olive). As the name implies, the Shell will usually have dark
brown or black bands. However, in some individuals these bands may be absent, if
present they can vary in number from between one and five. Adult snails have a reflected

lip around the shell aperture which is also dark brown in color. Shell shape is sub-

12

globose, imperforate, with aperture ovate-lunate. The adult shell will usually consists of
5 whorls and ranges from 18 — 24 millimeters in diameter (Backeljau et al., 2001; Burch,
1962; and Goodhart, 1962).
Rglroduction

Cepaea nemoralis is simultaneously hermaphroditic with cross-fertilization.
Mating between conspecifics is random, and multiple mating between different
individuals has been observed in a single mating season (Heller, 2001; and Murray,
1964). Cain and Currey (1968) reported that juvenile snails usually require two years to
reach reproductive maturity which is indicated by the reflected lip of the adult shell. In
the United Kingdom, C. nemoralis will lay eggs in early June with hatching in late June
and early July (Cain and Currey, 1963). Cepaea nemoralis is known to store sperm for
very long periods and any clutch of eggs produced could be the product of many matings
with different individuals (Murray, 1964). Eggs are laid in clutches, numbering up to 90,
and are buried just below the soil surface (Baur and Baur, 1993a). It may take up to 36
hours for an individual to produce one clutch (Wolda, 1967). These eggs can develop
and hatch within 2 — 3 weeks depending on environmental conditions. Eggs are oval and
measure 3.2 x 2.7 mm (Baur and Baur, 1993a). In Michigan, C. nemoralis has been
observed copulating and laying eggs as early as May and has been seen to mate at least
twice per year (pers. obs.). Cepaea nemoralis can live up to 7 years in the wild (B. Baur,
pers. comm.), possibly producing 900 eggs or more in their lifetime.
Habitat, Diet and Food Preference

Cepaea nemoralis is common in numerous habitat types, ranging from softwood

forests, sand dunes, grasslands, meadows, hedgerows, gardens, nettle patches, orchards,

l3

and vineyards (Cain and Currey, 1968; Chang, 1991; Godan, 1983; Goodhart, 1962; and
Richardson, 1975). In Europe it was reported that this Species is crepuscular, foraging
and feeding is generally nocturnal, while movement is limited during diurnal periods
(Cain and Currey, 1968; Martinson, 1999; and Speiser, 2001).

Williamson and Cameron (1976) reported that C. nemoralis, in the United
Kingdom, will feed on most plant material, however, it seems to prefer dead and
senescent herbs. Dead plants become softer and more palatable, while living plant tissue
had a harder external surface and an unfavorable taste (Williamson and Cameron, 1976).
These authors also found that herbs were preferred over grasses. They showed that herbs
compared to grasses contained more calcium and other essential minerals when compared
to grasses. These nutrient rich herbs would be important for Shell maintenance and
growth. Richardson (1975), and Wolda et al. (1971), in Europe, indicated that C.
nemoralis preferred dead and senescent plant material to living plants. It is interesting
that Richardson (1975) reported that C. nemoralis, from sand dunes, were not selective
with regards to herbs and grasses.

Chang (1991), in North America, reported C. nemoralis were very selective when
choosing food. This author reported that of the twenty plant species, collected from
habitats where C. nemoralis was found, ten (50%) were rejected when offered to
individuals within the laboratory, interestingly these ten plant species were the most
abundant. Chang (1991) also found that grasses were not accepted as food, and herbs
were preferred, which is similar to the finding of Williamson and Cameron (1976).

Shell Polymorphism

Cepaea nemoralis is perhaps best known for its highly polymorphic shell patterns.

14

In fact, the majority of studies published on this snail species explore the environmental
and genetic nature of this balanced polymorphism within and between populations of C.
nemoralis in both North America and Europe (Arnold, 1969; Brooks and Brooks, 1934;
Brussard, 1975; Brussard and McCracken, 1974; Cain and Currey, 1963a, 1963b and
1968; Cain et al., 1990; Cain and Sheppard, 1950 and 1954; Cameron, 1992; Clarke and
Murray, 1962; Cook, 1998; Cook et al., 1999; Currey et al., 1964; Davison, 1999;
Davison and Clarke, 2000; Diver, 1939; Goodhart, 1962; Heath, 1975; and Ozgo, 2005a).
Interpopulation variation is commonplace, in regards to color morphology and
number of bands present with C. nemoralis (Backeljau, 2001; Cain and Sheppard, 1954;
Currey et al., 1964; and Goodhart, 1962). Many different theories have been proposed to
explain the variation that occurs in wild populations. It was originally theorized that the
interpopulation variation that occured within small populations of C. nemoralis was
caused by genetic drift of non-adaptive genes ‘Sewall Wright effect’, thus, demonstrating
that selection was not involved (Diver, 193 9). It was later theorized that visual selection
of a predator caused interpopulation variation (Cain and Sheppard, 1954). More
specifically, that the primary selection pressures are the song thrush, T urdus ericetorum
Turton, 1807, and missel thrush, T. viscivorus (Linnaeus, 1758) (Cain and Currey, 1968;
Cain and Sheppard, 1950 and 1954; and Currey et al., 1964). Cain and Currey (1963)
later proposed that visual selection alone could not explain this variation. These authors
further suggested that ‘area effects’ or strong environmental forces, that were then
unknown, were involved. Climate, and its ability to change topography, has also been
implicated as a selection force (Arnold, 1969; Cameron, 1992; and Heath, 1975).

The current theory is that habitat is responsible for inter— and intrapopulation

15

variation (Ozgo, 20050 and 2005b). Ozgo was able to identify some of these ‘area
effects’ that eluded Cain and Currey in 1963. Ozgo, in Poland, demonstrated that habitat
type is the definitive selection force, and that banded C. nemoralis are found more often
in woodland habitats and that non-banded C. nemoralis are found in grassland and more
open habitats. The theory is that banded individuals are more susceptible to over heating
in grassland habitats where the radiant energy is greater and the dark bands cause the
shell to absorb more solar radiation. Further, non-banded individuals are less likely to
overheat in grassland habitats due to the absence of dark shell pigmentation and lighter
overall shell color. In general open habitats are less humid and have higher temperatures
while shaded habitats are more humid and have lower temperatures (Ozgo, 20050 and
2005 b).

The current study quantified the dispersal capabilities of C. nemoralis in two very
different habitats. One habitat was considered to be ‘high quality’ and was the epicenter
of this established C. nemoralis population. The other habitat was considered ‘low
quality’ and was adjacent to the high quality patch. If this population of C. nemoralis
was to spread naturally to the south and west individuals would have to traverse across
this sub-optimal patch. Control of C. nemoralis may become necessary if it were to
spread; therefore a control method was also tested. A commercially available
molluscicide (Sluggo® - iron phosphate) was used to test its usefulness at controlling a
large, established population of C. nemoralis. The molluscicide, iron phosphate, was
chosen because it is environmentally friendly and it is not a broad spectrum poison and
targets only molluscs (USEPA, 2005). This study also evaluated the efficacy of using

harmonic radar as a method to track terrestrial snails. Along with population dynamics

and distribution data this research is intended to provide insight into the natural dispersal,

spread, and control of an exotic, invasive, and pest land snail species.

CHAPTER 3: USING HARMONIC RADAR TO TRACK CEPAEA NEMORALIS
INTRODUCTION

Harmonic radar (HR) was developed in Switzerland and was first introduced in
1983 as a tool designed for detection of persons caught in an avalanche
(www.recco.com). An individual person carries a ‘reflector’ or transponder which is
integrated into their clothing or safety equipment. If an avalanche event occurs then it is
possible for rescue workers to locate victims buried under snow using an HR
transmitter/receiver. Range of detection is contingent upon transponder size (diode and
antenna length). Transponders used for rescue purposes can be detected from a distance
of several miles.

HR technology is ideal for tracking invertebrates due to the small size
transponders that can be built. In comparison, using a radio transmitter is not practical
with most invertebrates because transmitters are too large and heavy. It is possible,
however, to construct very small and lightweight HR transponders (~ 10’3 g) that can be
attached to almost any macroinvertebrate. Mascanzoni and Wallin (1986) were the first
to use HR technology for the tracking and detection of invertebrates (e.g. ground beetles).
HR technology has been used to track bumble bees, butterflies, caddis flies, honey bees,
land snails, moths, various dipterans, various ground beetles, and weevils (Carreck et al.,
1999; Brazee etal., 2004; Lovei et al., 1997 and 2003; O’Neal et al., 2004; Riley et al.,
1998 & 1999; and Roland et al., 1996). Lovei et a1. (1997) were the first to use HR to
track the movements of a land snail, Paryphanta busbyi watti Powell, 1946, in New
Zealand. What makes HR ideal for tracking otherwise cryptic invertebrates in their

natural environment is that it affords a high degree of tracking success with little

18

disturbance to their habitat.

Traditionally, ‘mark and recapture’ (MR) techniques have been employed to track
invertebrates. MR is a visual survey that requires going into the animals’ environment
for prolonged periods in order to relocate marked individuals and potentially disrupting
the habitat. MR is useful for determining population size and estimating the rate of
immigration and emigration in an animal population. The most commonly used method
for determining dispersal in land snails has been by using MR. The usual MR snail
method is conducted by marking individuals with nail polish, paints or dyes and releasing
them at a given starting point or at the place of capture, finding and recapturing them at a
later time, and then measuring the distances moved from that point over a period of time
(Cameron and Williamson, 1977; and Baur and Baur, 1993b) These MR methods, while
useful, do have limitations: (1) low recapture rates; (2) intrusive human movement in
and out of the snails natural environment; and (3) repeated sampling done over longer
time intervals can give a false idea of how snails actually move in their environment. As
a result the traditional MR methods are not very useful for determining dispersal.

HR is a tracking technique that allows the user to accurately track an organism in
their natural environment with minimal disturbance. Direct measurement of dispersal can
be done on a daily, weekly or seasonally. The current study is the first attempt to
measure land snail dispersal on a daily and weekly basis using harmonic radar. The
objective of this study were to calculate tracking success using HR techniques and
compare these findings to other studies that have used traditional method of mark and
recapture to relocate terrestrial snails, and to determine HR limitations.

AMTERlALS AND METHODS

The study site was located in Ingham County, Michigan (42°36.790’N
84°27.460’W) and is privately owned. Tracking of C. nemoralis was performed in a
favorable habitat (Snail Central) and in an unfavorable habitat (South Field). For a
complete description of these habitats please refer to Chapter 4 Materials and Methods.
Harmonic Radar

HR employs the use of a hand-held RECCO transmitter/receiver (RECCO Rescue
Systems, Lindingo, Sweden, www.recco.com) that transmits microwaves with a
frequency of 917 MHz. Two different types of HR tags (transponders) were used in this
study. The monopole (single wire) transponder was composed of two parts: (1) a
Schottky barrier diode (weight = 0.0046 g); and (2) a Teflon coated aluminum or iron
wire (Omega Engineering Inc., www.omega.com) of 0.10 mm (aluminum) or 0.25 mm
(iron) diameter and 8 cm in length. The dipole (double wire) transponder used the same
diode, mentioned above, but consisted of 2 wires (0.25 mm diameter), both 4 cm in
length, with the diode attached between them. The transponder receives power from the
microwave signal transmitted by the RECCO unit, the diode in turn doubles the
frequency of the Signal to that of the harmonic (1,834 MHz) which is then sent back to
the RECCO unit and converted to an audible beeping sound. The exact location of HR
tagged snails is determined by the intensity and direction of the audible signal.

In 2003 a total of 17 (15 adult and 2 juvenile) C. nemoralis were collected from
the study site. In 2004 and 2005 a total of 40 adult (20 in 2004, and 20 in 2005) C.
nemoralis were also collected from the study site and taken to Michigan State University
for HR tag attachment. The shells of collected snails were cleaned with a cotton swab

dipped in isopropyl alcohol and then wiped dry. HR tags were then glued to the surface

20

of the cleaned shell using superglue (Loctite Precision Super Glue®) and a small bead of
hot glue was then placed over the diode to help water proof and protect the diode from
damage. Nail polish was used to give each snail a unique identification code. To test the
usefulness of different style transponders one snail (in 2003) and eight snails (in 2004)
were tagged with dipole HR transponders. Snails were returned to the field the following
day and placed at the same location they were captured in 2003 or placed in either SC or
SF in 2004 and 2005. At the time of tracking the RECCO unit was held in hand and
turned clockwise and counter clockwise while sweeping it up and down and from left to
right in front of the user. This method maximized the detection ability of the RECCO
unit because the transponder will only work when receiving microwaves that are parallel
to the wire antenna.

Daily dispersal was tracked over a 14 day period from May 18-31”, 2003 in the
SC, and from June 5-18‘", 2004 and June 8-21”, 2005 in the SC and SF. Weekly and bi-
weekly dispersal was tracked from May — September 2003 and June — September 2004.
If snails were found dead they were removed from the study area. The tracking success
rate indicates the percent of C. nemoralis that were successfully tracked and found on
subsequent days and weekly collecting intervals. Therefore a tracking success rate of
75% would indicate that 75% of the snails tracked were recovered.
RESULTS
Pilot Studv 2003

Seventeen C. nemoralis were tracked daily from May 18-315‘ and then weekly and
bi-weekly from May — September 2003. The daily tracking success rate was 74.6%. Of

the individual snails a total of 5 individuals were tracked 100% of the time, and 3 were

21

tracked successfully 93% of the time. The weekly tracking success rate was 40.2%. The
l snail tagged with a dipole HR transponder had a daily tracking success rate of 100%.
During this period a total of 2 snails had dropped their HR tags and 4 had been killed
presumably by predators because the shells were either crushed or broken; a common
indication of a predator.
2&4

Twenty C. nemoralis (10 SC (Snail Central) and 10 SF (South Field)) were
tracked daily from June 5-18th and then weekly and bi-weekly from June — September
2004. The tracking success rates in the SC and SF were 77.1% and 91.5%, respectively.
Of the individual snails in SC a total of 5 individuals were tracked 100% of the time and
in SF a total of 9 individuals were tracked 100% of the time. The weekly tracking
success rates for SC and SF in 2004 were 43.6% and 51.8%. In SC a total of 5 snails
were tagged with dipole HR transponders and they had daily tracking success rates of
100%. In SF a total of 3 snails were tagged with dipole HR transponders and they had a
daily tracking success rate of 100%. During this study 3 snails died in SC and 1 snail
died in SF.
_2_0__’_5_

Twenty C. nemoralis (10 SC and 10 SF) were tracked daily from June 8-21”,
2005. The daily tracking success rates in SC and SF were 89.8% and 100%, respectively.
Of the individual snails in SC a total of 4 were successfully tracked 100% of the time and
in SF a total of 10 were successfully tracked 100% of the time. During this study 1 snail

died in SC and 5 snails died in SF.

Radar signals from dipole HR tagged snails could be detected from as far away as

22

10 m; monopole HR tagged snails could be detected up to 2 m. In 2003 and 2004 the
individual snails fitted with the dipole transponders were much easier to relocate and had
individual recapture rates of 100% during the daily recapture studies. Snails could be
located if they were buried 2 — 3 centimeters in the soil. Several HR transponders were
found in following years still attached to a broken shell and buried in the soil. In some
cases it was found that if the wire antenna became bent or crimped the detection distance
was greatly reduced to less than 1 meter. Some animals became hung up on vegetation if
they were tagged with a dipole transponder. It seems that the diode hanging off of the
animal free in space can catch on vegetation. This finding however was rare. In earlier
work done in 2003 hot glue was used to join the diode to the shell and in all cases this
failed and the transponders fell off within 1 — 2 days. Super glue was found to work
much better at joining the HR tags to the shell and in no cases did an HR tag ever fall off
using super glue.

At times no signal could be found for some of the snails even after a thorough
search of the Study site. In most cases the snail was relocated the following day within a
few meters from where it had been located previously. It was concluded that many of
these snails were climbing into the tree canopy and became undetectable using HR. If
these snails climbed high into the tree canopy they would be nearing the limit of
detection for the HR and in essence disappear from the study area. Even when
transponders were placed in trees several meters off the ground it was very difficult to get
any type of positive signal. This may be due to the angle at which the user is to the
transponder. It is essential for the HR user to become parallel to the transponder in order

to obtain a strong signal from the HR tag.

23

DISCUSSION

The tracking success in this study was much higher than the recapture rates
reported from studies on other land snail dispersal. Goodhart (1962) captured and
released 200 adult C. nemoralis, in England. Snails were then recaptured after 4 weeks,
13 weeks, and 1 year. This author calculated his recapture rates to be 66.5%, 54% and
41.5% afier 4 weeks, 13 weeks, and 1 year, respectively. Lamotte (1951) worked with C.
nemoralis, in France, from two different habitat types, garden and herb meadow. In the
garden habitat 20 C. nemoralis were marked, released at a central point, and recaptured
after 2 years. In the herb meadow 200 C. nemoralis were marked, and recaptured after 5
months. The garden and herb meadow the recapture rates were 4%, and 15%,
respectively. Schnetter (1951) performed a mark-recapture study on C. nemoralis, in
Germany, from two different habitat types, uncultivated meadow and scattered brushes.
In the uncultivated meadow 100 snails were marked, released at a central point, and
recaptured after 6 months. In the scattered brushes 100 snails were marked, and
recaptured after 2 years. The recapture rates of snails, for both habitat types, were 13%.

Baur and Baur (1990) tracked the movement of 807 marked Arianta arbustorum
(Linnaeus, 1758), in Switzerland, after one month and 3 months. They reported recapture
rates after one month and three months as 29.4% and 28.1%, respectively. Further, Baur
and Baur (1993b) tracked the daily movements of A. arbustorum in a clearing for 16
consecutive days, and in a vegetative belt 10 months after release, they reported recapture
rates of 47.5%, and 42%, respectively.

The snail tracking success rates of C. nemoralis in this study are the highest ever

reported. In this study the daily tracking success rates ranged from 74.6% - 100%. In

24

most scenarios all the snails could be found within 2 hours, demonstrating that HR is a
very good method by which to track terrestrial snails. Very little time was spent in the
animal’s habitat and thus little damage was done.

Harmonic radar does appear to have some limitations. In the rain it was difficult
to obtain a true positive signal and much of the ‘noise’ heard by the user was a false-
positive signal. A fair amount of noise was added because of the falling rain drops,
which are reflecting the radar signals and sending a false signal back to the receiver. HR
was not of much use if it was raining at the time of tracking. It was difficult to obtain a
signal from snails that had climbed into the tree canopy. This was probably the result of
the dense leaf canopy which impeded the HR signal, snails moving beyond the range
which the receiver could obtain a signal from the transponder, and the HR user not being
able to get in a parallel position to the transponder.

It was reported that HR was not very useful for tracking carabid beetles because
of several problems (O’Neal et al., 2004). O’Neal reported that beetles ofien became
hung up on vegetation and seemed to lack the physical strength needed to remove
themselves from the obstructions. Also, these authors had problems with HR tags falling
off the beetle elytra. This may be due to the use of hot glue and not super glue to join the
HR tag to the animal’s surface. In this study when hot glue was used to join the HR tags
to the Shell, all of them fell off within 1 — 2 days. However, when super glue was used,
the HR tags no longer fell off. Similar to what was found in this study O’Neal reported
that when the wire became bent the detection distance was greatly reduced. In 2005 all
HR tags were built with a much thicker (0.25 mm) wire and this seemed to reduce wire

bending because it was much more rigid. O’Neal reported less success with a thicker

25

inflexible wire, but this was not the case when tracking snails in this study.

Even though harmonic radar has some minor limitations it offers a very effective
method to track daily and weekly dispersal of land snails in a very detailed manner. This
method permitted the precise measuring of land snail movement with minimum
disturbance to their natural environment. Cameron and Williamson (1977) reported that
direct measurement of snails within their natural environment is difficult because it
requires continuous detailed mapping and frequent sampling. While the frequency of
sampling may not decrease with HR, the amount of time Spent in the environment does.
Precision of relocation, with minimum disturbance, made it possible to correlate
movements of land snails to a range of biotic and abiotic factors at the level of
microhabitat. HR will also prove useful for obtaining accurate dispersal distances
achieved by land snails, which could potentially impact how we control and manage
invasive land snail Species as well as conserve habitat for threatened and endangered

Species.

26

CHAPTER 4: DISPERSAL, POPULATION DENSITY AND DISTRIBUTION OF
CEPAEA NEMORALIS
INTRODUCTION

To become a successful invader, an organism must (1) move to a new location;
(2) establish a viable population; and (3) disperse from that locality (Mack, 2000; and
Shea and Chesson, 2002). How an organism spreads is a function of its dispersal
capabilities. Whether it establishes a viable population in a new area is a function of how
it responds to niche opportunities. The niche opportunities found in a new area are
greatly influenced by resource availability, natural enemies, and the physical environment
(Shea and Chesson, 2002). These three factors will also affect the invaders ability to
disperse beyond its established new location.

Dispersal is the capacity of an individual animal to move from the place of its
origin to new areas or away from centers of population density (Stiling, 1996). This is an
ecological process and selection tends to favor those individuals that move away from
their birthplace, and away from parents and siblings and thus utilize resources with less
competition from conspecifics. There are two types of dispersal; (1) long-distance, and
(2) short-distance. In their review of dispersal Shigesada and Kawasaki (2002) describe
the two types and introduce a useful terminology. Long-distance dispersal can be thought
of as rare, stochastic, and mediated by passive transport. Passive transport is facilitated
by naturally occurring phenomenon such as storms, water flow, rafting, and wind, as well
as agents such as other animals and humans (i.e. husbandry, cultivation, modification of
natural barriers, building of corridors, fragmentation, and commerce (Cohen, 2002;

Glassner-Shwayder, 1998; Harris and Silva-Lopez, 1992; and Mack et al., 2000)). Short-

27

distance dispersal occurs when offspring leave the area where they were born. This form
of dispersal depends upon the organisms own ability to move (i.e. walking, flying,
gliding, swimming, hopping, creeping, etc.). Land snails are often thought to have poor
short-distance dispersal capabilities (Heller, 2001). This long standing viewpoint of land
snail dispersal may be a reflection of the methodology used to determine snail dispersal.
It may also reflect stereotypes that snails are slow moving animals randomly wandering
through an environment.

It is essential to understand dispersal and life history of an exotic and invasive
animal if one wants to understand the rate at which it could potentially spread (Shigesada
and Kawasaki, 2002). Everything that is known about C. nemoralis dispersal has come
from a few published reports in Europe (Cain and Currey, 1968; Cameron and Wilson,
1977; Goodhart, 1962; Greenwood, 1974; Lamotte (1951); and Schnetter (1951)).
Interestingly, the dispersal of C. nemoralis has never been reported in North America
where this species is an exotic invader. While these European reports are useful, they
may seriously underestimate the dispersal capabilities of C. nemoralis. The mark and
recapture methods by which the dispersal was estimated in these studies are not accurate
because of low recapture rates. In addition, the time intervals between recapture events
are often very long, even exceeding one to two years. To truly understand dispersal of C.
nemoralis it is necessary to track this organism over Shorter time intervals (one day) to
reveal the subtle movements that are overlooked when snails are recaptured monthly or
yearly.

The population of C. nemoralis, established in Ingham County, Michigan, is

growing and most certainly viable. This population appears to have vast resources

28

available with regards to food and Shelter. Also, the physical environment (temperature
and humidity) which plays a vital role in affecting niche opportunities for this population
are also ideal. All land gastropods glide on a layer of mucus in order to move. It is also
very costly for the gastropod to produce mucus. Mucus is approximately 96 — 97% water
and the more mucus a land gastropod produces the more water it will lose (Baur and
Baur, 1990; and Denny (1980)). Williamson and Cameron (1976) found that C.
nemoralis will use 15% of the energy it acquires from food to produce mucus. When
physical conditions are not ideal C. nemoralis will become inactive and cease movement
so they can preserve valuable resources otherwise lost in mucus production (Cameron,
1970). This physiological dilemma could influence use of niche opportunities available
to C. nemoralis and decrease its rate of dispersal.

Baur and Baur (1993b) defined dispersal for a land snail to be “the distance
traveled by a snail in its daily activity during periods longer than one day”. Cepaea
nemoralis, and land snails in general, maintain a very intimate relationship with the
temperature, humidity, and habitats through which they move. To date no research has
been conducted using C. nemoralis to investigate the relationship among dispersal,
temperature, humidity and habitat on a daily basis. One explanation for this lack of
research has been that technology has never offered a means to track land snails
accurately and consistently. Currently a new method, harmonic radar (HR), is being used
and developed to track land snails and other invertebrates (Carreck et al., 1999; Brazee et
al., 2004; Lovei et al., 1997 and 2003; O’Neal et al., 2004; Riley et al., 1998 & 1999; and
Roland et al., 1996) (For a complete review of HR please see Chapter 3).

The objectives of the study are to (1) use HR to track the dispersal of C.

nemoralis in two distinct habitats and to investigate the relationship between dispersal,
temperature and humidity within each habitat; (2) measure the population density and
demographics to determine if this population is expanding; and (3) survey outlying areas
for C. nemoralis to ascertain its spread from the source population.

MATERIALS AND METHODS

The Study Site and Habitat

The study Site was located in Ingham County, Michigan (42°36.790’N
84°27.460’W) and is privately owned. The site was ten acres in size and was subdivided
into five distinct habitats designated as Snail Central, Blue Spruce, South Field, North
Field, and Homestead. These designations were based primarily upon vegetation
(Appendix A) and the mowing patterns of the homeowner (Figure 4.1). The total area
(m2) of each patch was approximated using aerial images obtained from the Michigan
Department of Natural Resources (www.mdnr.gov) and analyzed with Geo Express
Viewer with Mr. Sid® (www.1andsystems.com). The study area was formerly owned by
a commercial plant nursery.

The habitat called Snail Central (SC) was located on the southeast portion of the
site and was approximately 2,404 m2 in area. A total of 25 plant species were identified
in the SC (Appendix A). The SC had a closed canopy and the most abundant tree species
was green ash, F raxinus pennsylvanica; the most abundant herbaceous plant and ground
cover was poison ivy, Rhus radicans. The SC is considered the source of this established
population of C. nemoralis and is considered the ‘high quality’ habitat because of the
dense vegetation in the herbaceous layer. This dense layer maintains high humidity

levels at the surface of the ground which is favorable for land snail activity. The majority

30

of the soil surfaces in the SC receive no direct sunlight and most of the radiant energy of
the sun is filtered by the tree canopy and dense herbaceous layer.

The habitat called Blue Spruce (BSp) was adjacent to and west of the SC and was
approximately 4,882 m2 in area. A total of 22 plant species were identified in BSp
(Appendix A). The BSp had primarily an open canopy and the most abundant tree
species was blue Spruce, Picea pungens, and the most abundant ground cover was a mix
of R. radicans and various grasses (Poaceae).

The habitat called South Field (SF) was on the southwest portion of the site and
adjacent to the BSp and was approximately 23,734 m2 in area. A total of 20 plant species
were identified from the SF (Appendix A). The SF had no canopy and the only tree
present was F. pennsylvanica less than 2 meter in height. The ground cover of SF was
primarily a mix of various grasses, herbaceous, and woody plants. The SF is considered
the ‘low quality’ habitat because it lacks a tree canopy and does not have a dense
herbaceous layer. It is also deemed low quality because of the population density survey
of 2003. This type of habitat has the tendency to dry out during the day. Much of the
soil surface is directly exposed to the radiant energy of the sun.

The habitat called North Field (NF) was on the northwest portion of the Site and
was adjacent to and north of SF and was approximately 4,851 m2 in area. A total of 15
plant Species were identified from the NF (Appendix A). The NF had no canopy and no
trees were present, the ground cover of NF was primarily a mix of various grasses and
herbaceous plants.

The habitat called Homestead (HS) was on the northeast portion of the site and

was adjacent to and north of SC and BSp and was approximately 3,757 m2 in area. A

31

total of 6 plant Species were identified from the HS (Appendix A). The HS was
comprised of a maintained lawn around the homeowner’s house and had a partially
closed canopy comprised of silver maple, Acer saccharinum. The yard was a mix of
grasses.
Disp_e_rsa1

Harmonic radar (HR) was used to track daily and weekly dispersal (in meters) of
C. nemoralis over a 3 year period (For a complete review of HR and habitat types, see
Chapter 3). The year 2003 was considered a ‘pilot study’ and was used to develop a
methodology and to determine the efficacy of tracking land snails with HR. The years
2004 — 2005 were considered the definitive portion of the research which compared the
dispersal of C. nemoralis in two different types of habitat called Snail Central (SC); and
South Field (SF) - SC was considered to be ‘high quality’ habitat and SF was considered
to be ‘low quality’ habitat.

In 2003 at total of 17 (15 adult and 2 juvenile) C. nemoralis were collected in SC.
In 2004 and 2005 a total of 40 adult (20 in 2004, and 20 in 2005) C. nemoralis were
collected in SC. Adult snails were chosen as the focus of this research because the shell
is thick and the studies in Europe also examined the dispersal of adult snails. Juvenile C.
nemoralis have very thin shells, especially in the early spring, and those shells broke
when the transponder was glued to the shell. All C. nemoralis were captured by hand and
taken to Michigan State University for HR tag attachment. The Shells of collected snails
were cleaned with a cotton swab dipped in isopropyl alcohol and then wiped dry with
tissue paper. HR tags were then glued to the surface of the cleaned shell using superglue

(LOCTITE Precision Super Glue®). A small bead of hot glue was then placed over the

32

diode to help water proof and protect the diode from damage. Nail polish was used to
give each snail a unique identification code.

HR tagged snails were placed at the location of initial collection in 2003 from SC.
In 2004 — 2005 they were placed in either SC or SF at random starting positions; all
starting positions were marked with a flag that corresponded to the unique ID on
individual snails. Daily dispersal was tracked over a 14 day period from May 18-31”,
2003 in SC, and from June 5-18‘“, 2004 and June 8-21”, 2005 in SC and SF. Weekly and
bi-weekly dispersal was tracked from May — September 2003 and June — September
2004. If HR tagged snails were found dead they were removed from the study area.
When tracked snails were located the new position of the snail was marked with a flag
and the distance (in meters) in a straight line from the previous day’s location, and
direction moved (compass degrees) between the initial collection point and the recapture
point was determined. The percentage of time that C. nemoralis spent inactive (not
moving) from one day to the next or from week to week was calculated for the dispersal
studies in 2003 — 2005 in SC and SF. For the directionality data an individual snail could
move north (between compass points 315° — 45°); east (46° — 134°); south (135° — 224°);
or west (225° — 314°) (Appendix B).

In 2003 the air temperature (°C ), taken approximately one meter above the
ground, and the surface temperature, taken at the soil surface, were determined at the
time of snail recovery using a hand-held thermometer. In 2004 — 2005 HOBO
Dataloggers® were placed approximately 10 cm above the soil surface in SC and SF for
the entire sampling season to collect temperature (°C) and relative humidity (%) at 2 hour

intervals. The ‘daytime’ temperature and humidity was determined from the hours

33

between 7am and 7pm. The ‘nighttime’ temperature and humidity was determined from
the hours between 9pm and 5am. The ‘time of collection’ temperature and humidity was
determined from the l lam hour; a time when most tracking was conducted.

Population Density

During the late spring and early summer of 2003 the population density (number
of snails/m2) of C. nemoralis was determined for each habitat. At the time of sampling
an individual habitat, a ball was randomly thrown over the shoulder, and at the location
where the ball landed a hula hoop (WHAM-O®) was placed. The inside area of the hula
hoop was determined to be 0.5 m2. All C. nemoralis within the hula hoop area were
removed, placed into a plastic container, counted, and returned to the hula hoop area
when sampling was completed. The entire area within the hula hoop (litter layer, herb
layer, and shrub layer) was searched; trees were excluded. A total of 20 m2 (40 tosses of
the hula hoop) was sampled within SC, SF, Bsp, NF, and HS.

This sampling method was also used to sample the population density of C.
nemoralis again in the spring of 2005 for SC and SF only. In 2005 snails were identified
as either an adult (presence of peristome lip) or as juvenile (peristome lip absent), the
shell diameter was measured (mm), body color was noted (brown or yellow) and the
number of brown bands (1 - 5) on the shell were counted. Sampled snails were placed
into 4 size categories based upon the shell diameter: (1) Adult (> 20 mm); (2) large
juvenile (15 — 19 mm); (3) medium juvenile (10 — 14 mm); and small juvenile (< 9 mm).
Soil Chemistry

Soil samples were collected, using the protocol of the MSU. Soil and Plant

Nutrient Laboratory (SPNL), in SC and SF for comparative purposes. Samples were

34

submitted to the MSU. SPNL for analysis of soil pH, calcium (Ca), phosphorous (P),
potassium (K), magnesium (Mg), and nitrate-N.
Distribution

To determine the distribution of C. nemoralis in areas that surrounded the study
site a survey of outlying areas was performed during the summers of 2003 - 2005.
Roadway verges, public land and private property in the vicinity of the study area were
surveyed. Surveyed areas usually were composed of habitat suitable for C. nemoralis
and areas that could serve as a corridor for dispersal were also surveyed. A hunt-and-
pick method was used to survey for snails on the ground as well as looking for any Sign
of the snails on vegetation (fecal deposits), or empty and broken shells. The
latitude/longitude or township/range information was recorded for all sites surveyed.
Latitude and longitude was recorded using a hand-held GPS manufactured by Garmin®.
When referencing the township/range a method was used to denote the 40 acre parcel of
each section that was sampled. Each section denoted on a plat map is 640 acres. For this
study each section was subsequently divided into four 160 acre quadrants, and each
quadrant was divided into four 40 acre sub-quadrants. Therefore a notion such as
‘Section 29 SW/SE’ would indicate that the sample was taken in the southwest sub-
quadrant of the southeast quadrant of section 29.
Statistics

For the data collected in 2004 — 2005, a general linear model (GLM) was used to
find a relationship between dispersal (response variable - Y) and the temperature
(predictor variable - X1) and relative humidity (predictor variable — X2) at the time of

collection. The general a priori hypothesis for the GLM was Y ~ X, + X2. A GLM was

35

also used to examine the relationship between dispersal and temperature and to examine
the relationship between dispersal and relative humidity. A Student’s t-test was used to
evaluate differences in the dispersal, temperature (daytime, nighttime and time of
collection), and relative humidity (daytime, nighttime and time of collection) between SC
and SF. Chi-square (38) test of Independence was used to determine if snails moved in a
particular direction within the SC and SF. The dispersal (meter), temperature (°C), and
humidity (%) are expressed as a mean i 1 standard error (SE). Statistical analyses were
conducted using R v. 1.9.1®, Systat 11®, and EZ-Stat® for Windows.

RESULTS

Dismrsal

2003 Pilot Study:

A total of 17 (15 adult and 2 juvenile) C. nemoralis were tracked from May —
September 2003 in the SC (Appendix C). The mean (:1: 1 SE) daily air and soil
temperatures (°C) were 10.5 :h 1.1 and 13.0 i 0.85 (Figure 4.2). The mean daily dispersal
(meters) was 1.09 i 0.085 (Figure 4.3). The maximum and minimum dispersal by an
individual C. nemoralis in one day was 3.78 and 0.05 meter, respectively. The mean
weekly air and soil temperatures were 23.4 :t 0.86 and 21.2 i 0.93 (Figure 4.4). The
mean weekly dispersal was 4.07 i 0.99 (Figure 4.5). The maximum and minimum
dispersal by an individual C. nemoralis in one week was 24.9 and 0.07 meter,
respectively. During the 14 day trial C. nemoralis was found to disperse in a northerly
and easterly direction in the SC (x2 = 13.341, d.f. = 3, p = 0.00395). Cepaea nemoralis
did not disperse in a preferred direction during the weekly trial (7(2 = 5.247, d.f. = 3, p =

0.1545). Two individual C. nemoralis crossed from SC into BSp during the weekly

36

trials.
14 Day Temperature, Relative Humidity and Dispersal in the SC and SF 2004:

A total of 20 adult (IO/SC and 10/SF) C. nemoralis were tracked from June 5 —
18, 2004 in the SC and SF (Appendix D). The temperature (°C) and relative humidity
(%) data have been summarized in Table 4.1 and Table 4.2, respectively. The mean
daytime temperatures in SC (20.5) and SF (23.5) were significantly different (p <
0.0312). The mean daytime relative humidity (%) in SC (92.7) and SF (85.8) was
significantly different (p < 0.001). The mean nighttime temperatures in SC (17.8) and SF
(16.0) were significantly different (p < 0.001). The mean nighttime relative humidity in
the SC (95.8) and SF (98.1) was significantly different (p < 0.001). The mean
temperatures at the time of collection in SC (20.2) and SF (25.3), Figure 4.6, were
significantly different (p < 0.008). The mean relative humidity at the time of collection
in SC (94.3) and SF (83.0), Figure 4.7, was significantly different (p = 0.009).

The mean daily dispersal in SC (2.1) and SF (0.71) was significantly different (p
< 0.001), Figure 4.3; Table 4.7. Maximum and minimum daily dispersal by an individual
C. nemoralis in SC were (7.13 and 0.02 meter) and SF (4.59 and 0.02 meter). In SF there
was a relationship between dispersal and temperature and relative humidity at the time of
collection (GLM, F = 5.9911114, r2 = 0.1362, p = 0.0007). Further regression analysis
revealed that dispersal was related to humidity (GLM, F = 10.92.,116, r2 = 0.086, p =
0.0012) but not to temperature (GLM, F = 2.3041,.16, r2 = 0.019, p = 0.1318) Figures 4.8
and 4.9. The slope of the regression line for dispersal and humidity was positive in SF
(Figure 4.8), however the slope of the regression line for dispersal and temperature was

negative (Figure 4.9). There was no relationship between dispersal and temperature and

37

relative humidity at the time of collection in SC (GLM, F = 1.2491103, r2 = 0.0351, p =
0.295). Further regression analysis revealed that dispersal was not related to humidity
(GLM, F = 0.025L105, r2 = 0.0002, p = 0.8735) or temperature (GLM, F = 0.8613L105, r2 =
0.008, p = 0.3555) Figures 4.10 and 4.11. The slope of the regression line for dispersal
and humidity, and dispersal and temperature was positive in SC (Figures 4.10 and 4.11).
Frequency histograms of dispersal can be found in Appendix G. The percentage of time
that C. nemoralis spent not moving in SC was 3.6% and in SF was 14.0%. Cepaea
nemoralis was found to disperse in a westerly direction in the SC ()52 = 25.98, d.f. = 3, p <
0.0001). In SF C. nemoralis did not disperse in any preferred direction (x2 = 0.4266, d.f.
= 3, p = 0.9346). The percentage of tracked C. nemoralis that died before the study was
completed in SC and SF were both 10% (1/10). Daily dispersal figures for snails from
SC in 2004 and 2005 can be found in Appendix 1.

Weekly Temperature, Relative Humidity and Dispersal in the SC and SF 2004:

A total of 20 adult (IO/SC and 10/SF) C. nemoralis were tracked from June —
September 2004 in SC and SF (Appendix D). Temperature (°C) and relative humidity
(%) data have been summarized in Table 4.3 and Table 4.4, respectively. The mean
weekly daytime temperatures in SC (20.6) and SF (22.0) were significantly different (p <
0.0005). The mean daytime relative humidity in SC (88.1) and SF (84.9) was
significantly different (p < 0.0005). The mean nighttime temperatures in SC (16.7) and
SF (14.3) were significantly different (p < 0.001). The mean nighttime relative humidity
in SC (97.1) and SF (99.1) was significantly different (p < 0.001). The mean
temperatures at the time of collection in SC (20.0) and SF (22.0) were not significantly

different (p = .2016). The mean relative humidity at the time of collection in SC (86.6)

38

and SF (87.0) were not significantly different (p = 0.944).

The mean weekly dispersal in SC (4.98) and SF (3.06) were not significantly
different (p = 0.127), Figure 4.5; Table 4.7. The maximum and minimum weekly
dispersal by an individual C. nemoralis in SC were (17.32 and 0.66 meter) and SF (37.49
and 0.15 meter). There was no relationship between the dispersal and the temperature
and relative humidity in SC and SF (GLM, r2 = 0.0828, p = 0.298 and r2 = 0.0578, p =
0.3127, respectively). Frequency histograms of dispersal can be found in Appendix G.
During the weekly trial in SC C. nemoralis did not disperse in a preferred direction (x2 =
1.505, d.f. = 3, p = 0.68103). However, during the weekly trial in SF C. nemoralis did
move in a westerly and southerly direction (x2 = 8.533, d.f. = 3, p = 0.03618). The
percentage of time that C. nemoralis spent not moving in SC was 0.0% and in SF was
2.5%. The percentage of C. nemoralis that died before the study was completed in SC
was 22% (2/9) and in SF was 0.0%. One individual C. nemoralis crossed from SC into
BSp during the weekly trials.

14 Day Temperature, Relative H umidity and Dispersal in the SC and SF 2005:

A total of 20 adult (IO/SC and 10/SF) C. nemoralis were tracked from June 8 —
21, 2005 in SC and SF (Appendix E). The temperature (°C) and relative humidity (%)
data have been summarized in Table 4.5 and Table 4.6, respectively. The mean daytime
temperatures in SC (20.9) and SF (25.7) were significantly different (p < 0.001). The
mean daytime relative humidity in SC (96.6) and SF (72.6) was significantly different (p
< 0.001). The mean nighttime temperatures in SC (17.6) and SF (15.2) were significantly
different (p < 0.001). The mean nighttime relative humidity in SC (97.8) and SF (99.1)

was not significantly different (p = 0.3806). The mean temperatures at the time of

39

collection in SC (21.3) and SF (29.0) were significantly different (p < 0.001). The mean
relative humidity at the time of collection in SC (97.3) and SF (62.2) was significantly
different (p < 0.001).

The mean daily dispersal in SC (1.134) and SF (0.359) were significantly
different (p < 0.001), Figure 4.2; Table 4.7. The maximum and minimum daily dispersal
by an individual C. nemoralis in SC were (4.7 and 0.1 meter) and SF (1.83 and 0.0
meter). In SC there was a relationship between dispersal and temperature and relative
humidity at the time of collection (GLM, F = 4.5153,, . 1, r2 = 0.1028, p = 0.0023). Further
regression analysis revealed that dispersal was related to humidity (GLM, F = 4.867.)”,
r2 = 0.0412, p = 0.0294) but not to temperature (GLM, F = 2.581,”, r2 = 0.022, p =
0.111) Figures 4.16 and 4.17. The slope of the regression line for dispersal and humidity
was positive in SC (Figure 4.16), however the slope of the regression line for dispersal
and temperature was negative (Figure 4.17). There was no relationship between dispersal
and temperature and relative humidity at the time of collection in SF (GLM, F =
1.986394, r2 = 0.0596, p = 0.1213). Further regression analysis revealed that dispersal
was not related to humidity (GLM, F = 1.402196, 1'2 = 0.014, p = 0.2394) or temperature
(GLM, F = 1.332196, r2 = 0.0136, p = 0.2513) Figures 4.18 and 4.19. The slope ofthe
regression line for dispersal and humidity was positive in SF (Figure 4.18), however the
slope of the regression line for dispersal and temperature was negative (Figure 4.19).
Frequency histograms of dispersal can be found in Appendix G. C epaea nemoralis was
found to disperse in a westerly direction in SC (x2 = 7.455, d.f. = 3, p < 0.058). In SF C.
nemoralis did not disperse in any preferred direction (x2 = 4.262, d.f. = 3, p = 0.2344).

The percentage of time that C. nemoralis spent not moving in SC was 0.0% and in SF

40

was 27.5%. The percentage of C. nemoralis that died before the study was completed in
SC was 10% (1/ 10) and in SF was 50% (5/10). Daily dispersal figures for snails from SC
in 2004 and 2005 can be found in Appendix H.
Population Density and Demographics

The population density of C. nemoralis in 2003 for all patches was: SC (11.6/m2);
BSp (8.1/m2); SF (0.05/m2); NF (1.1/m2); and HS (0.65/m2) — Figure 4.20. In 2005 the
population density for SC and SF were 12.1 m2 and 0.0 m2, respectively. Cepaea
nemoralis in SC were found to have 5 different shell morphologies based upon the
number of bands present. Of the C. nemoralis identified in SC 86.3% had 5 bands;
10.8% had 4 bands; 2.1% had 3 bands; 0.4% had 2 bands; and 0.4% had 1 band (Figure
4.21). Two distinct body colors were also identified (brown or yellow) and 71.7% were
brown and 28.2% were yellow. The mean shell diameter for C. nemoralis in SC was 15.2
mm, a size within the juvenile range. The smallest adult and largest juvenile snail
identified in SC had a Shell diameter of 18 mm and 22 mm, respectively. The age
distribution of C. nemoralis in SC was 85.1% juvenile and 14.9% adult (Figure 4.22).
The most abundant Size class in SC for 2003 was the medium juvenile (10 — 14 mm) C.
nemoralis (Figure 4.23). The most abundant size class in SC for 2005 was the large
juvenile (15 — 19 mm) C. nemoralis (Figure 4.24). A large number of snails died off
before reaching adult size and the numbers of small juveniles were underrepresented in
the population sampling (Figures 4.15 and 4.16).
Distribution

A total of 33 sites were surveyed outside the boundary of the study site for the

presence of C. nemoralis (Appendix F). Of these survey sites only one (Hunt’s Verge)

41

was found to have C. nemoralis. Hunt’s Verge was directly across the road (Hagadom
Rd.) from SC. Numerous times the broken shells of C. nemoralis were found along the
east and west verges of Hagadom Rd. in direct proximity to SC.

DISCUSSION

C epaea nemoralis individuals have greater daily dispersal capabilities in the high
quality habitat (SC) than in the low quality habitat (SF). During the daily ‘daytime’
hours of 2004 and 2005 SC had significantly higher relative humidity than did SF.
Cameron (1970) demonstrated that C. nemoralis become much less active when the
relative humidity is low (65%). In SF where the mean ‘daytime’ humidity ranged from
72.6 (2005) — 87% (2004), C. nemoralis would spend less time moving and more time
closed down with an epiphragm. Cameron (1970) suggested that C. nemoralis would
remain inactive at low humidity levels once the epiphragm had been laid. However, in
SC, where the mean ‘daytime’ humidity ranged from 88.1 (2004) — 96.6% (2005), C.
nemoralis were more active, dispersed greater distances and rarely produced an
epiphragm.

The importance of moisture is more evident in 2005 than in 2004. The year 2004
had more rain events than did the year 2005. For much of the daily tracking, in 2004, it
was either raining at the time of collection or had rained the previous night. In the year
2005 it was warmer and drier with fewer rain events. Rain events in 2004 helped keep
the mean ‘daytime’ humidity levels in SF at or above 85% while in 2005 the mean
humidity level in SF never exceeded 72.6%. Dispersal of C. nemoralis was greater in
2004 than in 2005 from both SC and SF.

In Europe it was reported that C. nemoralis have a preferred temperature range

42

(19 — 20 °C) in which they remain active (Godan, 1980). In SC the mean ‘daytime’
temperature never exceeded 20.9 °C over a three year period at the soil surface and
dispersal was higher. However, in SF the mean ‘daytime’ temperature was as high as
25.7 °C in 2005. This showed the importance of temperature in the dispersal of this snail
species. When snails were under favorable conditions (low temperature and high
humidity) they tend to disperse greater distances and remain active longer. This was true
for both SC and SF, in 2004, a high rain event year. In 2004 the mean ‘daytime’
temperature in SF ranged from 22 — 23.5 °C, temperatures above the preferred range for
C. nemoralis, however this cohort of snails remained active throughout the year and
dispersal was not significantly different from SC during the weekly assessment. This was
most likely due to the mean daytime relative humidity being as high as 85.8%. Cameron
(1970) has shown that during times of high humidity C. nemoralis will remain active
even if the temperature is high. In comparison, SF in 2005 had a mean ‘daytime’
temperature of 25.7 °C and a mean ‘daytime’ humidity of 72.6% and C. nemoralis was
much less active and dispersed over shorter distances.

In 2005, the hot, dry year, there was a strong relationship between C. nemoralis
dispersal and temperature and humidity in SC. In the SC the mean ‘time of collection’
temperature (21.3 °C) and humidity (97.8%) were high in comparison to SF where no
relationship of dispersal to temperature (29.0 °C) and humidity (62.2%) was found. In
2004, the wet and rainy year, there was a strong relationship between C. nemoralis daily
dispersal and the temperature and humidity in SF. Even though the mean ‘time of
collection’ temperature (25.3 °C) was high the humidity was also high (83.0%) in SF. No

relationship was found in SC where the mean ‘time of collection’ temperature (20.2 °C)

43

was ideal and the humidity was high (94.3%). Finding no relationship in SC
demonstrates that C. nemoralis will disperse actively when conditions were ideal (low
temperature and high relative humidity). When temperature was high (above the ideal)
and humidity was high there is a correlation between dispersal and temperature and
humidity (2005 SC and 2004 SF).

In all years for both SC and SF increases in dispersal were associated with
increases in humidity (Figures 4.25, 4.27, 4.29 and 4.31) and decreases in dispersal were
associated with increases in temperature (Figures 4.26, 4.28, 4.30 and 4.32). In SF 2004
and SC and SF in 2005 the slopes of the regression lines were negative for dispersal and
temperature (Figures 4.9, 4.17 and 4.19). Temperature negatively effects dispersal
especially if the temperatures were high and above the ideal range. In SC and SF 2004
and in SC and SF 2005 the Slopes of the regression lines were positive for dispersal and
humidity (Figures 4.8, 4.10, 4.16 and 4.18). Humidity was a very important factor
driving the dispersal of this species. High humidity often could offset the negative
effects of high temperature. Even under conditions when the temperature was high snails
would still disperse if the humidity was also high (Figures 4.27 and 4.28). Dispersal
activity was greater in SC than in SF because the humidity levels were higher in SC and
temperatures were usually higher and humidity lower in SF. Many more snails remained
active and were dispersing in SC while snails were inactive and dispersed less (Appendix
G).

These results support the finding that C. nemoralis do have an optimum
temperature range (19 — 20 °C) in which they are active. If the temperature is ideal and

the humidity is high then C. nemoralis will disperse. It is clear that C. nemoralis

44

dispersal is closely linked to environmental temperature and humidity and that these two
parameters are greatly influenced by the structure of that environment (vegetation).
Cepaea nemoralis will disperse more often when the humidity is above 83% even if the
temperature is high, and this is evident from the daily results in 2004 from SF. If the
temperature is ideal and the humidity is above 86% then C. nemoralis are very active and
disperse greater distances and this is evident from weekly results from 2004 in SC and
SF.

Snail Central, in all 3 years of this study, produced the ideal physical conditions
required for C. nemoralis dispersal. Conversely, SF only produced ideal physical
conditions during times of frequent rain events. Therefore, SF was a barrier to C.
nemoralis dispersal and would only become a viable corridor if the conditions were right
and rain was frequent.

It has often been cited in the literature that C. nemoralis are primarily nocturnal
with little diurnal activity (Cain and Currey, 1968; Martinson, 1999; and Speiser, 2001);
however in the present study it was found to have diurnal activity. If C. nemoralis
activity was a function of temperature and humidity than it seemed nocturnal activity
would have been greater in SF rather than SC. At night SF became significantly cooler
and more humid than SC in 2004 and 2005. If activity of C. nemoralis was primarily
nocturnal then one would expect the activity to be greater in SF than in SC where at night
the conditions are more optimal (low temperature and high humidity). However, in both
habitats mean ‘nighttime’ temperature was below the established ideal range of 19 — 20
°C. The mean ‘nighttime’ temperature in SF ranged from 14.3 — 16 °C during 2004 and

2005. In SC, the mean ‘nighttime’ temperature ranged from 16.7 — 17.8 °C during 2004

45

and 2005. It seemed the lower, and the higher the temperature was from the ‘ideal’ range
the less active C. nemoralis became regardless of humidity levels. These results and field
observations would suggest that C. nemoralis may not be nocturnal, and that diurnal
activity does take place. If C. nemoralis were dependent upon optimum ranges of
temperature and humidity than the ‘ideal’ conditions are present more often during the
day than at night in SC and SF. These physical characteristics of SC and SF would then
promote diurnal activity.

It has been reported that brown shelled and banded C. nemoralis are found more
often in wooded and shaded habitats than their yellow shelled and non-banded
morphological counterpart which were found in grassy and open habitats (Jones et al.,
(1977); Ozgo (2005a and 2005b). Cain and Curry (1968) reported that dark brown
morphs were much more frequent in nettle patches than in grassland habitats. These
authors reported that yellow and pink shelled C. nemoralis were more common in the
grasslands. Brown shelled and banded individuals are more susceptible to over heating in
grassland habitats where the radiant energy is greater and the darker color causes the Shell
to absorb more solar radiation. Further, yellow and non-banded individuals are less
likely to overheat in grassland habitats due to the absence of dark shell pigmentation and
a lighter overall shell color (Ozgo, 2005a and 2005b).

In the present study 97.1% of C. nemoralis identified in the SC had either 5 bands
or 4 bands and 71.7% had brown bodies. This is suggestive of a morph that would be
common to woodland areas possessing shade. The SC is wooded, shaded, and has a
dense herbaceous layer while SF is an open habitat with very little shade. Only one C.

nemoralis was ever found in SF during the population density sampling of 2003 and

46

2005. All SF C. nemoralis used in this dispersal study came from SC.

If C. nemoralis morphology did play a role in activity then it is plausible that
individuals tracked in SF overheated at the higher temperatures and therefore had
decreased activity levels. The phenomenon of overheating is more evident from SF in
2005 where 50% of C. nemoralis being tracked died within the first week. The daily
temperature during the day in 2005 from SF often exceeded 40 °C. Ozgo (2005b)
Showed that yellow shelled C. nemoralis were more active at low (70%) humidity levels
and that brown shelled C. nemoralis are active when humidity levels are high. This
polymorphic banded dilemma of C. nemoralis population found in SC may also have
acted as a barrier to further dispersal beyond that area.

What made SC an ideal habitat for C. nemoralis was the dense herbaceous layer,
primarily composed of poison ivy, Rhus radicans. This author feels that the dense layer
of vegetation was important in keeping the moisture levels high at the surface of the
ground by keeping moisture trapped there and slowing down evaporation. The SC also
had a tree canopy which shades a major portion of that habitat. According to Ozgo
(2005a), adequate Shade decreased the amount of solar radiation reaching the ground and
reduced overheating. In stark comparison SF was comprised of various grasses and
shade was almost nonexistent. The type of vegetation in SF was not conducive to
maintaining high moisture levels at the soil surface thus contributing to the dryness of SF
during the day. Banded C. nemoralis in this type of habitat would absorb much more
solar radiation and overheat as a result of exposure. The niche opportunities for C.
nemoralis were decreased in SF due to the physical conditions of that habitat. Therefore,

C. nemoralis dispersal was greatly reduced outside SC because of poor physical

47

characteristics (low humidity and high temperature).

Several soil nutrients (Ca, Mg, P, N, K) and soil pH are important factors that
shape gastropod communities (Burch, 1955, Lozek, 1962). Areas depauperate in these
soil nutrients are usually void of gastropods. Calcium carbonate is an essential soil
nutrient and has been correlated to the presence of gastropods in the environment (Lozek,
1962). Soil nutrients varied only slightly between SC and SF (Table 4.8); therefore soil
nutrients and pH were not used as variables to differentiate SC and SF. Both habitats
were considered of suitable quality for C. nemoralis based upon these soil nutrients and
soil pH.

Goodhart (1962) attempted to determine the population density and dispersal of
C. nemoralis from the Hundred Foot Bank in England. Two-hundred individuals were
captured, marked and released, and then recaptured afier four weeks, 13 weeks, and one
year, and the distances moved were calculated. This author found that snails moved on
average 0.18 m (4 weeks), 1.1 m (13 weeks), and 3.02 m (1 year). Goodhart considered
this a low rate of natural dispersion. From these calculations he estimated that only 3%
of adult C. nemoralis would disperse 10.97 m in 4 years. Also, it was determined that the
density of C. nemoralis was 3.5/m2. Recapture rates were 66.5%, 54% and 41.5% after
four weeks, 13 weeks, and one year, respectively.

Lamotte (1951) worked with C. nemoralis in France from two different habitat
types, garden and herb meadow. In the garden habitat 20 C. nemoralis were marked,
released at a central point, and recaptured after two years; the snails moved an average
9.7 m. In the herb meadow 200 individuals were marked, and recaptured after 5 months;

the snails moved an average 8.1 meter. In the garden, and herb meadow snail recapture

48

rates were 4%, and 15%, respectively.

Schnetter (1951) performed a mark-recapture study on C. nemoralis in Germany.
Two different habitat types were studied: uncultivated meadow and scattered brushes. In
the uncultivated meadow 100 snails were marked, released at a central point, and
recaptured after six months; the snails moved an average 23.8 m. In the scattered brushes
100 snails were marked, and recaptured after 2 years; the snails moved an average of 32.1
m. The recapture rates of snails, for both habitat types, was 13%.

Cain and Currey (1968) reported migration rates of C. nemoralis within a
quartered testing plot comprised of various grassland species. These plots also had nettle
patches between the boundaries of the four quadrants. These authors found that the
emigration from nettle patches to the surrounding grassy areas was low (2.9 - 8.6%),
even though population densities in nettle patches were high. Conversely, emigration
from grassy areas to nettle patches was high (5.6 - 35.2%), even though the population
densities in grassy areas were low. Cain and Currey (1968) suggested that perhaps nettle
patches were more suitable habitats because predators (birds) could be avoided.

Cameron and Williamson (1977), in England, estimated the migration rates of C.
nemoralis from a grassland habitat. These authors reported that 26 — 56% of C.
nemoralis migrated, however they did not directly measure the dispersal distances
achieved.

The dispersal rates of C. nemoralis, at the study site in Michigan, were the highest
ever reported. For example, Goodhart (1962) estimated that adult C. nemoralis, in
England, would not disperse more than 12 yards in 4 years. The results of the present

study are drastically different from that reported by Goodhart. In SC adult C. nemoralis

49

were found to have a mean dispersal of 4.98 m/week (2004) and 2.1 m/day (2004).
Individual snails were also found to disperse great distances over the course of a single
day. In SC an individual C. nemoralis moved 7.13 meters in a single day. The snail
moving the greatest distance between collecting periods was from SF. In SF an
individual C. nemoralis moved 37.49 meter in 11 days! While this distance was
impressive, at least from the standpoint of a snail, it is possible that this individual was
carried by a predator or moved by a bird. However, it rained for many of days between
tracking events and had rained the night before this snail was recovered.

It may be that the dispersal capabilities of C. nemoralis in Europe are reportedly
so low because the techniques used were not sufficient for estimating dispersal.
Goodhart (1962), Lamotte (1951) and Schnetter (1951) all utilized mark and recapture
techniques to estimate dispersal. Mark and recapture is useful for determining
immigration and emigration as well as population density based upon the proportions of
marked snails to unmarked snails. It is not, however, effective for determining dispersal.
Lamotte (1951) reported that C. nemoralis would disperse 9.1 m/2 years and concluded
this by a recapture rate of 4%; Lamotte (1951) also reported C. nemoralis would disperse
8.1 m/5 months and concluded this with a recapture rate of 15%. Schnetter (1951)
reported C. nemoralis dispersal to be 23.8 m/6 months and 32.1 m/2 years both estimates
were based upon a recapture rate of 13%. The work of Goodhart (1962) was based on
recapture rates that ranged from 41.5 — 66.5%. The daily tracking success (habitat and
year) in the present study was 74.6% (SC 2003), 77.1% (SC 2004), 91.5% (SF 2004),
89.8% (SC 2005), and 100% (SF 2005).

Cepaea nemoralis in SC are a source population. No other populations of C.

50

nemoralis were found in surrounding areas (Appendix F). It is not known how this
population was introduced. It has been suggested that perhaps this population was
brought to this location by a local nursery. At one time a local nursery owned and
operated part of its business at this location and was responsible for planting the trees in
SC. The trees were planted some time in the late 1980’s to early 1990’s. The property
was sold to the current landowner’s in 1994. So it is feasible that this population of C.
nemoralis was introduced to SC when trees were planted over a decade ago.

If C. nemoralis were to spread naturally beyond SC it would encounter many
barriers. For the population to spread to the East it would have to cross an adjacent road
(Hagadom Rd). It is not impossible for C. nemoralis to cross this type of obstacle and
two adult individuals were found in the verge on the opposite side of the road. However,
this verge is one meter in width and beyond it is a mowed lawn. No individuals were
ever found East beyond the verge directly across the road from SC. If C. nemoralis were
to spread to the North and South they would encounter well maintained and mowed
lawns. No C. nemoralis were ever found to the South of SC and only a few were found
to the North in the homestead (HS) habitat. Individual C. nemoralis found in HS were
most likely moved there via human activity because the children that lived at this private
home often played with the snails. If C. nemoralis was to spread to the West it would
have to move through the blue spruce (BSp) habitat and then traverse across SF for
several hundred meters before encountering a woodland habitat. Even though some C.
nemoralis have been found in SF and the north field (NF) to the west of SC no
individuals were been found in the woodland area beyond. During 2004 C. nemoralis did

disperse over 3m/year in SF the conditions required to obtain these dispersal distances

51

were frequent rain storms. It was concluded that SF was a Sink and any C. nemoralis that
venture there would most likely die before ever reaching the woodland area beyond.

This population has failed to spread beyond SC for 2 reasons: (1) surrounding
habitats are not optimal (i.e. grassland) and even hazardous to C. nemoralis (i.e.
manicured lawns and roads); and (2) there is a morphological barrier (i.e. being banded
and having dark pigmentation in the body) that this population is currently unable to
overcome. The selective advantage of being banded and dark in color would be to
survive in shaded habitats. The SC was an ideal habitat for this particular C. nemoralis
morph to survive, reproduce and multiply. But, SC is land locked and is essentially an
island for this population of C. nemoralis. In three years of tracking in SC only 3 snails
ever crossed over into BSp which is adjacent to SC and separated by approximately 2
meters of mowed grass.

Baur and Baur (1992) reported that once land snails reached the edge of a habitat
they are unwilling to travel into the sub-optimal area beyond. Instead snails either travel
along the edge or turn back into the original habitat. Cepaea nemoralis seem to do both
(edge follow and turn back) when they encountered the border of SC. This phenomenon
can be likened to ‘ping-pong’ in that when C. nemoralis reach the margin of SC they
bounce back towards the interior or travel along the edge rather than pass into the habitat
beyond. In SC C. nemoralis encountered a mowed path to the west which if crossed
would lead to BSp. To the North and South were mowed lawns and to the East is an area
of tall grasses approximately 5 meters in width which lead to the adjacent road (Figure
4.1). All outside areas surrounding the perimeter of SC were considered sub-optimal to

SC and therefore C. nemoralis would be unlikely to move into that area unless conditions

52

were very good at the time of dispersal (e.g. raining). Currently, no corridor exists that
would link SC to the adequate habitats beyond. This was due primarily to human
activity, however if this activity were to change corridors could be created allowing a

route by which C. nemoralis could spread beyond SC.

53

Table 4.1. The mean (:1: SE) daily daytime, nighttime, and time of collection
temperature (°C) for Snail Central and South Field 2004 taken at the height of 10

cm using a HOBO datalogger.

 

 

M Snail Central South Field
Mean temperature (range) Mean temperature (range)
Daytime 20.5 i 0.39* (9.8 — 27.5) 23.5 :t 0.65* (4.5 — 36.5)
Nighttime 17.8 :1: 0.34'1' (10.2 - 23.6) 16.0 i 0.461" (3.3 — 22.1)
Time of Collection 20.2 i 1.06; (10.9 — 25.1) 25.3 d: 1.441 (12.9 — 32.3)

 

"' Significantly different (Student’s t-test, t = -2.169, d.f. = 204, p < 0.0312).
'1' Significantly different (Student’s t-test, t = 3.152, d.f. = 204, p < 0.001 ).
1 Significantly different (Student’s t-test, t = -2.855, d.f. = 26, p < 0.008).

54

Table 4.2. The mean (3: SE) daily daytime, nighttime, and time of collection
relative humidity (%) for Snail Central and South Field 2004 taken at the height of

10 cm using a HOBO datalogger.

 

 

M Snail Central South Field
Mean relative humidity (range) Mean relative humidity
(range)
Daytime 92.7 d: 0.78* (57.3 - 100) 85.8 :1: 1.64* (31.9 - 100)
Nighttime 95.8 i 0631' (78.0 - 100) 98.1 i 0.331‘ (87.7 - 100)
Time of Collection 94.3 t 1.44; (79.4 — 100) 83.0 :1: 3.77: (53.2 — 100)

 

* Significantly different (Student’s t-test, t = 4.269, d.f. = 204, p < 0.001).
'1' Significantly different (Student’s t-test, t = -3.209, d.f. = 138, p < 0.001).
1 Significantly different (Student’s t-test, t = -2.788, d.f. = 26, p = 0.009).

55

Table 4.3. The mean (i SE) weekly daytime, nighttime, and time of collection
temperature (°C) for Snail Central and South Field 2004 taken at the height of 10

cm using a HOBO datalogger.

 

 

29% Snail Central South Field
Mean temperature (range) Mean temperature (range)
Daytime 20.6 :t 0.17* (8.6 - 30.3) 22.0 d: 0.25”“ (4.1 — 34.8)
Nighttime 16.7 :t 0.16? (9.0 — 23.6) 14.3 d: 0191' (3.7 — 22.1)
Time of Collection 20.0 :1: 1.221 (15.2 - 26.3) 22.0 :1: 0.871 (17.9 - 26.3)

 

* Significantly different (Student’s t-test, t = -4.542, d.f. = l 160, p < 0.0005).
‘1’ Significantly different (Student’s t-test, t = 9.861 , d.f. = 827, p < 0.001).
I Not significantly different (Student’s t-test, t = -1.331, d.f. = 16, p = 0.2016).

56

Table 4.4. The mean (:1: SE) weekly daytime, nighttime, and time of collection
relative humidity (%) for Snail Central and South Field 2004 taken at the height of

10 cm using a HOBO datalogger.

 

 

2004 Snail Central South Field
Mean relative humidity (range) Mean relative humidity
(range)
Daytime 88.1 :1: 0.44* (50.5 — 100) 84.9 :h 0.65“ (40.4 — 100)
Nighttime 97.1 i 0.191' (77.5 — 100) 99.1 at 0131' (84.6 — 100)
Time of Collection 86.6 d: 2.981 (69.6 — 100) 87.0 :1: 4.631 (67.7 — 100)

 

* Significantly different (Student’s t-test, t = 4.051, d.f. = 1160, p < 0.0005).
1' Significantly different (Student’s t-test, t = -6.9032, d.f. = 828, p < 0.001).
I Not significantly different (Student’s t-test, t = -0.0705, d.f. = 16, p = 0.944).

57

Table 4.5. The mean (t SE) daily daytime, nighttime, and time of collection
temperature (°C) for Snail Central and South Field 2005 taken at the height of 10

cm using a HOBO datalogger.

 

 

A5 Snail Central South Field
Mean temperature (range) Mean temperature (rangeL
Daytime 20.9 i 0.40"“ (12.1 — 30.0) 25.7 i 0.77* (9.0 — 42.0)
Nighttime 17.6 d: 0391' (10.2 — 23.2) 15.2 :t 0.611" (4.5 — 22.8)
Time of Collection 21.3 :1: 0.881 (16.0 — 25.9) 29.0 d: 1.36: (20.9 — 38.3)

 

* Significantly different (Student’s t-test, t = -5.542, d.f. = 194, p < 0.001).
‘1' Significantly different (Student’s t-test, t = 3.336, d.f. = 138, p < 0.001).
1 Significantly different (Student’s t-test, t = -4.677, d.f. = 26, p < 0.001).

58

Table 4.6. The mean (:h SE) daily daytime, nighttime, and time of collection
relative humidity (%) for Snail Central and South Field 2005 taken at the height of

10 cm using a HOBO datalogger.

 

 

M Snail Central South Field
Mean relative humidity (range) Mean relative humidity
Gauge)
Daytime 96.6 i 0.49* (78.0 — 100) 72.6 d: 2.13* (32.9 — 100)
Nighttime 97.8 :1: 1.421 (92.2 — 100) 99.1 :1: 0.361 (80.0 — 100)
Time of Collection 97.3 i 0.751 (91.8 -— 100) 62.2 i 4.031 (43.4 — 100)

 

* Significantly different (Student’s t-test, t = 10.941, d.f. = 194, p < 0.001).
'1' Not significantly different (Student’s t—test, t = -0.879, d.f. = 138, p = 0.3806).
1 Significantly different (Student’s t-test, t = 8.577, d.f. = 26, p < 0.001).

59

Table 4.7. The mean (i SE) daily and weekly dispersal (meter) of C. nemoralis

from SC in 2003 and from SC and SF in 2004 and 2005.

 

 

Snail Central South Field

Mean dispersal Mean dispersal
D_ailx
2003 1.09 :1: 0.085 N/A
2004 2.1 :t 0.16* 0.71 :t 0.075*
2005 1.134 :1: 0.0921“ 0.359 i 0.0431
Weekly
2003 4.07 :t 0.99 N/A
2004 4.98 i 0.771 3.06 :1: 0.911

 

* Significantly different (Student’s t-test, t = 7.861 , d.f. = 223, p < 0.001).
'1' Significantly different (Student’s t-test, t = 6.736, d.f. = 21 1, p < 0.001).
1 Not significantly different (Student’s t-test, t = 1.543, d.f. = 71, p = 0.1271).

60

Table 4.8. Soil nutrients and pH from SC and SF 2005.

 

 

Soil Nutrient Snail Central South Field
Calcium 1,167 ppm 1,082 ppm
Magnesium 176 ppm 172 ppm
Potassium 118 ppm 293 ppm
Phosphorous 28 ppm 55 ppm
Nitrate-N 0.9 ppm 2.5 ppm
Soil pH 6.0 6.4
Lime Index 68 70

 

61

 

Figure 4.1. Map outlining the 5 distinct patches (snail central, blue spruce, south field,

north field, and homestead) within the study area in Ingham County, Michigan.

62

Temperature (C)

 

“5%“ A
‘4 \ m

\Vfl

v

 

\N
\

#

 

\K

 

j—c—airtemp -
1 +soi1 temp 5—

 

film——

ONhQOOO
L.

'i— __

I Y I j T T ' i i 1

5/18 5/19 5/20 5/21 5/22 5/23 5/24 5/25 5/26 5/27 5/28 5/29 5/30 5/31

Date

Figure 42. Air and soil temperature (Celsius) taken over a 14 day period
(5/18/2003 - 5/31/2003) in the SC.

63

Dsipersal (m)

H

p
m

 

sc (2003) sc (2004) SF (2004) SC (2005) SF (2005)

Location (Year)

Figure 4.3. The mean daily dispersal (i 1 SE) of C. nemoralis from SC in
2003 and the SC and SF in 2004 and 2005. .

64

30

gig/1W \\

 

 

 

 

 

 

 

 

 

g 20
‘5
E 15 1
“at 1 fl
E 10 i—O—air temp 1
[+5011 tempi
5 i
O i T I 1 I I l T
6/1 1 6/26 7/1 1 7/26 8/10 8/25 9/9 9/24

Date

Figure 4.4. Weekly air and soil temperature (Celsius) taken from 6/11/2003 -
9/26/2003 in the SC.

65

Dispersal (m)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

SC 2003 SC 2004
Location (Year)

Figure 4.5. The mean weekly dispersal (i 1 SE) of C. nemoralis from SC in 2003
and the SC and SF in 2004.

66

Temperature (C)

351I

N
C
A

30 .
25 M 4\

M

/\\

MW
/Mo
/ \ //

 

M

\V/

 

 

O

 

+ SC Temperature L—
1+ SF Temperature

 

 

 

 

f

f I T fl

6/6 6/7 6/8 6/9 6/10 6/11 6/12 6/13 6/14 6/15 6/16 6/17 6/18

Date

Figure 4.6. Temperature (Celsius) taken at ground level over a 14 day period

(6/05/2004 - 6/18/2004) in the SC and SF.

67

 

 

 

 

 

 

 

 

 

100
,. 80
‘3: /r\—./‘\/
g 60 ‘7
5 1 1+ SC Relative Humidityi
:1: 40 — r .~——
2 1 .+ SE Relative Humidity 1
E 20 1e - 4
5 1
0 if T T I i | 7 r r r r

 

6/5 6/6 6/7 6/8 6/9 6/10 6/11 6/12 6/13 6/14 6/15 6/16 6/17 6/18
Date

Figure 4.7. Relative Humidity (%) taken at ground level over a 14 day period (6/05/2004
- 6/18/2004) in the SC and SF.

68

 

Kit
1

 

 

 

 

 

4.5 « .
4 . y = 0.0169x- 0.6653
:5 35 4 R =0.086l .
3 3 p=0.0012 . .
E
a 25 , . o .
:3 i 0
3' 2 i 0 1 O '
E 1.5 4‘ . . z . .
I d; . O : . A
1 . - 0
0.5i ‘ ‘ ‘ , 3
i V f O 4 T r ‘ 1
40 50 60 70 80 90 [00

Relative Humidity (%)

Figure 4.8. Regression analysis of C. nemoralis daily dispersal and relative
humidity (%) from SF in 2004.

69

{I}

. i l

4.5 y = -0.028x+ 1.4619 0
41 R’=0.0195

A I _
E 3'51 p—0.l3l8 .
3 3," O .
g .
TV; 2.5 'i O .
S 2~ 9 °
9 1 t 0 3 °
25 L5 1

0.5 i,

".00.
‘0

0
t3.
.0
-- O
F“

0 5 10 15 20 25 30 35

Temperature (Celsius)

Figure 4.9. Regression analysis of C. nemoralis daily dispersal and temperature
(celsius) fiom SF in 2004.

70

00
_._l

 

 

7 1 y = 0.0697x- 4.4329 °
1 0
6.1 R’=0.0002 ,9 .
’5 1 p=0.8735
{‘5 51 i
E 1 3 ’ t o o
'5. 4 ‘ 0 ° 8 ’
qr331 : ° 0 r
.11 1 0 ° ° 0 S
Q I
2 1 . O
o “ 3
1 - z 8 ’0
1 i *7 § 0
1 O .. O Q 0
0 3 v i . rQL—o—Q——+—9
75 80 85 90 95 100

Relative Humidity (%)

Figure 4.10. Regression analysis ofC. nemoralis daily dispersal and relative humidity
(%) from SC in 2004.

71

Dispersal (meters)

--° N DJ A U! 0‘ \J 00
n1_ __1 __ _J__ ___..L__2 .__I_ F. J___,.__l____ LL___J

O

y = 0.0811x+ 0.3681

R2 = 0.008 0
p = 0.3555

 

0

Temperature (Celsius)

Figure 4.11. Regression analysis of C. nemoralis daily dispersal and temperature
(celsius) from SC in 2004.

72

Temperature (C)

 

 

/‘<

 

 

 

 

 

 

1
10 1 1 .
' 1 + SC Tenpeiature1
5 1 1 —I— SF Terrpelature _
0 i l l I I i 1 7 I 1
6/19 6/29 7/9 7/19 7/29 8/8 8/18 8/28 9/7 9/ 17

Date

Figure 4.12. Weekly ten'pelature (Celsius) taken at ground level from 6/25/2004 -
9/15/2004 in the SC and SF.

73

 

 

 

 

 

 

 

 

 

100 1 —
i4 1 /\\ f
2? 90 ‘
E
S 1
j/ \V x
>
E 70 . X v
a 1 . . 1
60 1 1+sc Relative Humidity *_
1 1+sr Relative Humidity1
50 i T I .' 1 1 i 1 1 T.
6/19 6/29 7/9 7/19 7/29 8/8 8/18 8/28 9/7 9/17
Date
Figure 4.13. Weekly relative humidity (%) taken at ground level from 6/25/2004 -

9/15/2004 ill the SC and SF.

74

 

 

 

 

 

 

 

 

 

 

 

 

 

40
35 , —
525174>*‘*\e\;t44\\\//
as
320 W
E 15 .
I— 1 J (I
10 1- 1+scremp1—
5 1+SF Tempf—
O 1 1 1 i 1 fl 1 r

 

T f

6/8 6/9 6/10 6/11 6/12 6/13 6/14 6/15 6/16 6/17 6/18 6/19 6/20 6/21

Date

Figure 4.14. Temperature (Celsius) taken at ground level over a 14 day period

(6/08/2005 - 6/21/2005) in the SC and SF.

75

Relative Humidity (%‘

1101

100 ‘W : W
90

 

 

 

 

 

 

 

 

 

 

 

 

 

80 / \

7O / \ g

60 / \ Wm )'
501\ v \f \ /
40; V '—o—SCHumidi U
301 +SFHumidJ'

 

 

 

201T fl ' T ‘ ' 1 r 1 f 1 1 1

6/8 6/9 6/10 6/11 6/12 6/13 6/14 6/15 6/16 6/17 6/18 6/19 6/20 6/21
Date

Figure 4.15. Relative Humidity (%) taken at ground level over a 14 day period
(6/08/2005 - 6/21/2005) in the SC and SF.

76

 

 

 

l
x o
4.5 1 y = 0.0737x-6.0962 0
1 R2 =0.0413 ’ 0
g 3.5 1' p = 0.0294
“g 3 1 ° 3
Z’ 25 i ’
cu ° ‘ O
E 2 i O . . .
.Z.’ = O
g 1.5 l
l l 9 8 o 4.???
i.” O
05 i ‘ . Q . O
0 i 1 ‘1 1 ; .1 g .T ’ 1 1
90 9] 92 93 94 95 96 97 98 99 100
Relative Humidity (%)

Figure 4.16. Regression analysis of C. nemoralis daily dispersal and relative
humidity (%) fi'om SC in 2005.

77

Dispersal (meters)

y = ~0.0465x+ 2.0908

 

 

 

4.5 4‘ 0
l o , R2=0.0223
3.5 7 p=0.lll
3 1
2.5 J.
2i
1.5
1 ~;
0.5 1
o 4 a
15 17 19 21 23 25 27

Temperature (Celsius)

Figure 4.17. Regression analysis of C. nemoralis daily dispersal and temperature
(celsius) from SC in 2005.

78

to
__ _1
O
0

L8 1
1.6 1 y =0.0035x+0.l402
l
E? 1.47 :’ o R2=0.0144
o I = 7
g 1.2? p 0...394
‘1 11 ’ °
8 9 o . 0 o
§°3i 8 o

00.0

_J.___Jt,
O
O
O

 

 

D
O O O
N J:- 0‘
i.
’
00 9+ 0

O

50 60 70 80 90

Relative Humidity (%)

J}.
C

Figure 4.18. Regression analysis of C. nemoralis daily dispersal and relative
humidity (%) from SF in 2005.

79

g 4» 0 Jo.

 

1-3 i y = -0.0096x+ 0.6398 0 ’
1.6 l 2-
A . R —0.0137 . o
E 1.441 p=0.25l3 ’ O
3 1.2 1
E 1 J 00 .

a 1 9 O 0
g 0.8 1 . . . .’
07 *l O .0; 0 o
0‘ T T *7 13 g’ .’ 3 5‘

0 5 IO 15 20 25 30 35
Temperature (Celsius)

Figure 4.19. Regression analysis of C. nemoralis daily dispersal and temperature
(celsius) from SF in 2005.

80

 

2

 

 

 

 

 

N umber ofCepaea /m

 

 

 

 

Snail Central Blue Spruce South Field North Field Homestead
(11.6/m2) (8.1/m2) (0.05/m2) (1.1/m2) (0.65/mZ)

Habitat

Figure 4.20. Specific patch and population density (snails/m2) of C.
nemoralis in 2003.

8]

4 Bands (10.8%)

 
 
  
   
 

:‘ 3 Bands (2.1%)

2 Bands (0.4%)

1 Band (0.4%)

5 Bands (86.3%)

Figure 4.21. The number of bands present (percentage of population) in C.
nemoralis from the SC in 2005.

82

 

Adult (14.9%)

 

Juvenile (85.1%)

Figure 4.22. The percentage ofjuvenile and adult C. nemoralis fromthe SC
in 2005.

83

Size Class

    
  

 

D > 20 run (Adult)
j I 15-19 mm(Large juvenile)
C] 10-14 am (rredium juvenile)

I < 9 mm (small juvenile)

l
‘
l
l
l
1
l

 

 

 

 

0 20 40 60 80 100 120

Number of Snails

Figure 4.23. The distribution of C. nemoralis by size class (adult, large juvenile, medium
juvenile and small juvenile) fiom the SC in 2003.

84

140

 

l El>20mn(Adult)

I l5—l9mn(l.argejuvenile) .

I l0-l4mn(Medium

' venile
I < 9 11m (Srmll juvenile)

 

 

 

 

Size Class

 

T l

0 20 40 60

8 l
é
Q

Number of Snails

Figure 4.24. The distribution of C. nemoralis by size class (adult, large juvenile, medium
juvenile and srmll juvenile) fromthe SC in 2005.

85

Dispersal (meters)

 

 

 

4 v 120
1 l
3.5 + l
T ‘K T 100
3 +
! ' 80
2.5 T j
l ,
21 T60
1.5 i 1 . ‘ !
{ T—t—Mean d1spersal/dayi i 40
1 T 1 + Relative humiditLT l
. ' 20
0.5 + l
i 1
1 l
0 i T 1 F T 1 j 0
l 2 4 3 6 7 8 9 10 ll 12 l3 14
Day

Figure 4.25. The mean daily dispersal (meters) of C. nemoralis and relative humidity (%)

from SC in 2004.

86

Relative humidity (%)

Dispersal (meters)

N 1*"
MWMA

N

—

 

 

j l

T i”
l I
i T 20
j 1

1L i”
l

i no
.L . . T i

i l + Mean dispersal/day 1 T

7L [—9- Tenperature (C) j i 5
j T T1 1 l T V 7L .# # fi 1 fij 0

 

 

Day

Figure 4.26. The mean daily dispersal (neters) of C. nemoralis and temperature (celsius)
from SC in 2004.

87

Temperature (celsius)

 

 

 

1.6 T T 120
l
1.4 T i
T A T 100
1.2 T l
g l T T 80
g i }
7,, osT T 60
1% 0.6 l
a T T 40
0.4 + . . l
T T—t—Mean dispersal/day! i 20
031 T—o—Relative humidity l 1
1 A .
0 . 4 1 T 1 . T . A 0

Day

Figure 4.27. The mean daily dispersal (meters) of C. nemoralis and relative humidity (%)
from SF in 2004.

88

Relative humidity (°/o‘

Dispersal (meters)

  
   

  

1.4 " T. 30
1.2 ‘ A
j 25 3
1 ‘ 7‘”,
20 3
0.8 - E
15 g
0.6 ‘ a.
E
0.4 , ‘—-t—Mean dispersal/day, 10 ‘—

. 1+Te erature (C)
0.2 f mp 5
l 2 3 4 5 6 7 8 9 10 ll 12 l3 14
Day

Figure 4.28. The mean daily dispersal (meters) of C. nemoralis and tenperature (celsius)
from SF in 2004.

89

1 1
2 1 T 105
”g? T i 100
'5 l 5
E l + 95
1
§ 1 +
a I 190
l 1
0.5 T 1+Mean dispersal/day" 1 85
1 TLC—Relative humidity 1 T
1 .
0 1 1 r g 1 a? 1 1 80

 

 

 

 

 

Day

Figure 4.29. The mean daily dispersal (meters) of C. nemoralis and relative humidity
(%) from the SC in 2005.

90

Relative Humidity (%‘

Dispersal (meters)

 

 

5" T 30

l l

T l

T + 25

1 2:
1 12° '—
1 l i"
T i 15 g
T 1
T 1- 10 2'
1 r 7 . E—
; T+Mean dispersanayi 1 5
T—o—Temperature(C)J 1

 

 

—T
O

1234567891011121314
Day

Figure 4.30. The mean daily dispersal (meters) of C. nemoralis and temperature
(celsius) fromthe SC in 2005.

91

0.7 T T 120

  
 
 

 
 
  

 

 

  

 

0.6 T 1 100
l
7,? 0.5 1
E 1 ~~ 80
35: 0.4 '
.3 -- 60
g 0.3
Q.
~”—’ + 40
a 0.2 1 T . fl
1 j + Mean drspersal/dayT
0.1 1 T +Relative humidity l * 2°
0 1 T T r T a 1 A 1 T T; T 0

 

Figure 4.31. The nean daily dispersal (neters) of C. nemoralis and relative humidity
(%) fiom SF in 2005.

92

Relative humidity (%'

 

 

07 T T 45
i 40
.0 T
1 + 35
A 0.5 T T E
3 : T '5
°’ 0.4 - ‘ ‘ 3
E . 25
(U ., .
'3 .T 20 E
T a
5 l 1 15 E
02 T f 7 T 1—
: T—t—Mean dispersal/day: T 10
0-1 1 1+ Terrperature (C);1 1 5
0 1 fl 1 1 1 f 1 1 4V 1 1 i 1 —Jr‘ 0

 

Figure 4.32. The mean daily dispersal (meters) of C. nemoralis and terrperature
(celsius) from SF in 2005.

93

CHAPTER 5: CONTROL OF CEPAEA NEMORALIS
INTRODUCTION
Control of Pest Gastropods

Because of their recognized pest status around the world in greenhouses, gardens,
viticultures, grasslands, forests, and in agriculture many control strategies for land
gastropods have been designed using a wide variety of chemicals, physical barriers, traps,
and biological controls (Godan, 1983; Barker, 2002; and UCIPM, 2006). Some of the
more common molluscicides used to control land gastropods are metaldehyde ((CH3-
CHO)4) — derived from polymerization of acetaldehyde), isolan (1 -isopropyl-3-methyl-5-
pyrazolyl dimethylcarbamate), cloethocarb ((2-(2-chloro-lmethyloxyethoxy)phenyl
methylcarbamate)), and methiocarb (4-methylthio-3,S-xylyl-N-methylcarbamate). These
toxins can be applied as either sprays, baits, or broadcast upon the ground, and enter the
snail’s body by ingestion or through dermal contact (Henderson and Triebskom, 2002).
Once these chemicals contact the land gastropod they act as irritants and desiccants, and
if ingested they inhibit metabolism and have neurotoxic effects.

Molluscicide toxins are broad spectrum and can affect a wide range of vertebrates
and invertebrates. For example, carbamates (isolan, cloethocarb, methiocarb) are
cholinesterase inhibitors and allow accumulation of acetylcholine causing loss of muscle
tonus in the intoxicated animal (Henderson and Triebskorn, 2002). Any animal that uses
acetylcholine as a neurotransmitter can be effected by this toxin. Metaldehyde can cause
the release of the neurotransmitter gamma-aminobutyric acid (GABA) which is an
inhibitory neurotransmitter. GABA is produced to block the signals sent from one cell to

another in the central nervous system. In gastropods metaldehyde causes convulsions or

94

seizures. Metaldehyde is also an irritant to the gastropod and causes the animal to
produce large amounts of mucus. Increasing mucus production is a defense against the
irritant, but at the same time it will cause desiccation through water loss.

Other strategies have been developed to control land gastropods. Citrus growers
in California are using copper sheathing to girdle the bases of trees (Martinson, 1999;
Sakovich, 2002). Cepaea nemoralis, and land snails in general, seem unable to traverse
across a barrier made of copper. It is thought that the mucus trail left by the gastropod
reacts with the copper to produce a small electrical charge (UCIPM, 2006). This method
is a deterrent and does not harm the snail but it can prevent them from reaching the tree
canopy and fruit. Traps have been used such as boards placed upon the ground and
attract land gastropods which are subsequently crushed and destroyed. Also, traps
containing beer are useful in attracting and killing snails within small gardens. However,
most traps are not very effective in controlling large populations and require a high
degree of maintenance.

Carnivorous snail species like Rumina decollate (Linnaeus, 175 8) and Euglandina
rosea (Ferussac, 1821) have been used as a biological control to eat pest Cantareus
aspersus (Mueller, 1774) in California and Achatinafulica (Achatinidae) in Hawaii
(Hadfield et al., 1993 and Sakovich, 2002). The parasitic nematode, Phasmarhabditis
hermaphrodita (Schneider, 1859), has also been used to control pest gastropods.
Biological controls that have been used for several African land snail species, include
predaceous flatworms (Geoplana septemlineata Hymen, 1939, and Platydemus
manokwari de Beauchamp, 1962), carnivorous snails (Edentulina aflim’s Boettger, 1913,

Gonaxis quadrilateralis Preston, 1910, and Streptaxis kibweziensis Smith, 1894), hermit

95

crabs (Coenobita sp. and Birgus sp.), and rats (Rattus spp.) (USDA-APHIS, 2005).
Parasitoids such as sarcophagid flies, Sarcophaga spp. have been used to control white
snails, T heba pisana (Muller, 1774) and Cernuella virgata (de Costa, 1778), and conical
snails, Cochlicella spp., in southern Australia (Baker, 2002). Other predators of land
gastropods include Coleoptera (Carabidae and Lampyridae) and Hymenoptera

(F orrnicidae) (Rant and Barker, 2002).

California citrus growers have implemented a program of integrated pest
management (IPM) that utilizes several methods to control for pest snails in orchards.
This IPM calls for the (l) spraying of a commercial molluscicide in infested areas; (2)
citrus trees are skirt pruned removing those branches that contact the ground; (3) copper
barriers are installed around tree bases; and (4) introduction of R. decollata after
molluscicide break down to eat any pest snails lefi within the treated area (Sakovich,
2002). This approach is having positive results in the orchards of California.

Martinson (1999), reported C. nemoralis as a pest of vineyards in Ontario,
Canada. This author reported that C. nemoralis was easily controlled by using Prozap®
2% Metaldehyde in the grape canopy. In most cases applying large quantities of a
molluscicide can have positive effects on controlling pest populations. What makes most
molluscicides undesirable to use is the impact they can have on non-target species
including hmnans. These toxins can kill indiscriminately and have long lasting effects on
non-target wildlife. Increasing awareness of pesticide contamination and its
environmental impact is forcing a search for less harmful means of pest control. New
molluscicides such as iron phosphate have recently been developed which are less toxic

to wildlife.

96

Iron Phosphate

Because iron phosphate is a less toxic molluscicide it was chosen for a short-term
experimental trial to determine the efficacy of this bait/molluscicide to kill and eradicate
C. nemoralis. The SC was used because of its high population density of C. nemoralis
(For more information on habitat description and population density please see Chapter
4). A bait containing 1% iron phosphate (F ePO4) was chosen because of its recognized
toxicity to molluscs and that it has no observable effect on wildlife (mammals, birds, fish,
non-target insects, and aquatic invertebrates) while generally regarded as safe for food
use and non-toxic to humans (USEPA, 2005). Iron phosphate is naturally occurring in
nature as a solid, and will not readily dissolve in water. When consumed by the
gastropod iron phosphate inhibits calcium absorption in the gut and will quickly halt the
feeding process. Intoxicated gastropods usually die within 3 — 6 days post-consumption
(USEPA, 2005).

Iron phosphate was approved for use by the ERA. in 1997 (E.P.A. Reg. No.
67702-3-54705) and commercially produced by W. Neudorfi‘ GmbH KG, Germany, and
distributed in the United States by Lawn and Garden Products, Inc. It is known by the
trade name Sluggo® and commonly sold at garden and home improvement centers. It is
known to control both slugs and snails (Deroceras reticulatum, D. laeve, Arion
subfitscus, A. circumscriptus, A. hortensis, A. rufus, A. ater, Limaxflavus, L. tenellus,
Ariolimax columbianus, Helix spp., Helicella spp., and Cepaea spp.). The purpose of this
study was to test the efficacy of iron phosphate as a chemical control agent for a large,
established population of pest C. nemoralis.

[MATERIALS/1ND METHODS

97

Study Design
In 2005 the 2,404 m2 site (SC) was divided into 15 equal size plots of 10 X 10

meters (Appendix 1). Within each 10 X 10 plot a smaller 3 X 3 meters (9 m2) sub-plot _
was established and designated as the treatment zone. Flags of two different colors were
used to designate plot and sub-plot boundaries. Plots were then grouped into five blocks
(A, B, C, D, E — Appendix I) each containing three of the 10 X 10 meter plots. The 3 X 3
meter sub-plot was used as the area for treatment application. Each plot within a block
was assigned a treatment (bait, no bait, and sham bait) by using a random number
generator. Bait and sham bait was applied to each treatment zone at the manufacturers
recommended amount of 1 1b./1,000 r12 (= 48.4 gram/9 m2). A total of 0.45 Kg Sluggo®
was purchased from a local nursery at a cost of ~ $17 US. A total of 500 grams of sham
bait was obtained from the manufacturers of Sluggo®. Sham bait contained the
attractants of the bait, but was missing the active ingredient iron phosphate. The
manufacturer provided enough sham bait for two treatments.

A pre-application population density survey was performed within each of the 15
3 X 3 meter sub-plots to get baseline information on the number of C. nemoralis present
in each area. Each time the population density was sampled a hula hoop (WHAM-O®)
was randomly tossed within each 3 X 3 meter sub-plots for a total of 3 times. The inside
area of the hula hoop was determined to be 0.5 m2. All live and dead snails within the
area of the hula-hoop were counted. All dead snails were removed from the 3 X 3 meter
sub-plots. Bait and sham bait was applied to each treatment zone every week for two
weeks. One week afier the first treatment applications were applied the population

density of C. nemoralis was again assessed from within the 3 X 3 meter sub-plots, and

98

the following day bait and sham bait were re-applied. After the second week the
population density of C. nemoralis was again determined. At the time of sampling a
thermohygrometer was used to measure the temperature (°C) and relative humidity (%) at
the soil surface from within each 3 X 3 meter sub-plot.
Symptoms of Intoxication

To study symptoms of intoxication by iron phosphate 20 (7 adult and 13 juvenile)
C. nemoralis were exposed to iron phosphate in a small laboratory experiment. C.
nemoralis were collected fi'om SC and placed into a plastic container and starved for 7
days. After starvation five snails were placed into a plastic container with approximately
2.5 cm of moist soil and bait pellets. Enough pellets were placed in the container to
cover most of the surface area to ensure immediate contact with the snails. Snails were
allowed to feed for one hour and then they were removed and placed into another
container with only moist soil. Behavior of intoxicated snails was observed for up to an
hour and then checked every day for seven days to determine when death had occurred.
Statistics

A general linear model (GLM) 2-way Blocking ANOVA was used to evaluate
blocking effect and differences in the number of live snails and the number of dead snails
among treatments. Further evaluation between treatments was done using a l-way
ANOVA and Tukey’s post-hoe test. One-way AN OVA and Tukey’s post-hoe test was
used to evaluate differences in the temperature and relative humidity among the blocks.
x2 Test of Independence was used to determine if there was an increase in the number of
dead snails found in each treatment between week one and week two. Statistical analyses

were conducted using R v. 1.9.1® and Systat 11® for Windows.

99

RESULTS

Post-ApplicationJOne Week)

The number of live and dead C. nemoralis recovered from each treatment zone has been
summarized in Table 5.1. The number of pre-treatment live snails was not significantly
different among blocks (GLM, F = 0.424112, p = 0.664), Figure 5.1. There is no evidence
for differences in the number of living C. nemoralis among blocks (GLM 2-way
ANOVA, F = 2.8113,”, p = 0.2094). There is no evidence for differences in the number
of living C. nemoralis among treatments (GLM 2-way ANOVA, F = 2.81 13,”, p =
0.0888). There is no evidence for differences in the number of dead C. nemoralis among
blocks (GLM 2-way ANOVA, F = 2.73 3,] 1, p = 0.9083), but there is evidence for the
differences in the number of dead snails between treatments. Significantly more C.
nemoralis were found dead in the bait treatment than in the sham bait treatment (p =
0.042, Tukey’s test). Just under half (41.8%) of all C. nemoralis surveyed in the bait
treatment was found to be dead (Table 5.1). The physical parameters (temperature and
humidity) among the blocks were not different except for Block A which was
significantly warmer than the other 4 blocks (p < 0.05; Table 5.2).

Post-Appfilicatim (Two Weeks)

There is no evidence for the differences in the number of living C. nemoralis
among blocks (GLM 2-way ANOVA, F = 1.196311 1, p = 0.219). There is no evidence for
differences in the number of living C. nemoralis among treatments (GLM 2-way
ANOVA, F = 1.1963,; 1, p = 0.3565). There is no evidence for differences in the number
of dead C. nemoralis among blocks (GLM 2-way ANOVA, F = 5.80131 1, p = 0.6482),

but there is evidence for the differences in the number of dead snails between treatments.

100

Significantly more C. nemoralis were found dead in the bait treatment than either the no
bait (p = 0.00378, Tukey’s test) and sham bait treatment (p = 0.00479, Tukey’s test).
Their was a significant increase in the number of dead snails found in the bait treatment
between week one and week two (352 = 9.305, d.f. = 1, p = 0.0022). No significant
increase in the number of dead snails was found in the no bait treatment (x2 = 2.276, d.f.
= 1, p = 0.1313) or the sham bait treatment (x2 = 1.80, d.f. = 1, p = 0.1797) between week
one and week two. Over three-quarters (75.6%) of all C. nemoralis surveyed in the bait
treatment was found to be dead (Table 5.1). The physical parameters (temperature and
humidity) among the blocks were not different (Table 5.2).
DISCUSSION

Iron phosphate is an effective molluscicide for killing C. nemoralis. Significantly
more C. nemoralis were found dead in the bait treatment than in the no bait or sham bait
treatments. The number of dead snails between week one and week two in the baited
areas increased significantly from 41.8% to 75.6%. Iron phosphate killed more adults
than it did juveniles indicating the bait may target older snails. No evidence was found to
indicate that the number of living snails was different or decreased among the treatments
or between week one and week two. This finding indicates that C. nemoralis moved
between treatments and has a high population density (See Chapter 4). Plots were
adjacent to one another and snails could move in and out of treatment zones. Reservoirs
(i.e. trees) for living snails may have also played a role in no net decrease in the number
of living snails. The number of living snails in the sham bait treatments actually
increased from week one to week two (Table 5.1) indicating the presence of a snail

reservoir.

lOl

The symptoms of intoxication for C. nemoralis in the lab are consistent with the
Sluggo® literature. However, in the lab intoxicated snails do seem to lose some muscle
tonus. Loss of muscle tonus was seen when intoxicated snails would show lethargy and
hang the foot and part of the body outside the shell. In some cases the snail would not
retreat back into the shell even if poked with forceps and probe. Many intoxicated snails
would retreat into their shells and never again emerge with death following within six to
seven days. Juvenile snails seemed to die faster than adult snails and the adults would
feed longer on the bait sometimes for an entire hour.

I concluded that iron phosphate is an effective chemical that can be used to
control a large pest population of C. nemoralis. This study was carried out at the
manufacturers recommended application of 0.45 Kg/92.9 m2. The manufacturers
suggested amount was meant to be used in small gardens and not in an area with dense
vegetation. In dense vegetation, similar to the SC, adequate coverage is not obtained
using the manufactures suggested amount. It was shown that iron phosphate can kill C.
nemoralis, however, the density of this population was not significantly impacted by use
of the bait. To significantly decrease the number of C. nemoralis in a large, wild
population more iron phosphate would need to be used. It is the recommendation of this
author that the quantity of bait being applied to infested areas be increased to at least 1.8
Kg bait/92.9 m2. One set-back to using iron phosphate to control a large population is the
cost. The amount of iron phosphate needed to treat 1 acre is approximately 4.54 Kg at a
cost of $42 U.S./4.54 Kg (Baute and DiFonzo, unpublished). Baute and DiFonzo have
suggested that Sluggo® is too expensive for use on field crops. However, iron phosphate

even applied at 4 times the manufacturers recommended application amount would still

102

be a worthwhile investment to control isolated populations of C. nemoralis. Bait
containing iron phosphate can last in the environment for up to one week (personal
observation). After a weeks time the pellets begin to break down and become covered
with a white fungus.

What makes iron phosphate an ideal molluscicide even with the high cost is that
does not have an impact on mammals, birds, fish and aquatic invertebrates. In this study
no other animals were found dead within the sampled areas. Iron phosphate seems to be
target chemical product having an impact only on molluscs. One fall back to using iron
phosphate is that it cannot discriminate between native and pest gastropods. However,
this is an acceptable trade-off when one considers the toxicological effects of other

molluscicides.

103

Table 5.1. The mean :1: SE of live and dead C. nemoralis found before treatment
and during week one and week two post-application, the total number of adults
and juveniles found in each treatment group and the percent dead C. nemoralis

after treatment for SC in 2005.

 

 

Treatment Number of live Number of dead Total C. nemoralis
C. nemoralis C. nemoralis (% dead)
Pre-Apglication
Bait 12.4 i 3.6 NC“ 62
No Bait 11.6 :1: 3.] NC 58
Sham Bait 8.8 i 1.6 NC 44
Post-Anglication
(1 Week)
Bait 5.0 :1: 1.7 3.6 :t 0.67 43 (41.8%)
13 A'l' 12 A 25 (48.0%)
12 J: 6 J 18 (33.3%)
No Bait 8.2 :l: 2.1 1.4 i 0.67 48 (14.5%)
18A 2A 20(10.0%)
23 J 5 J 28 (17.8%)
Sham Bait 2.4 i 0.7 0.6 i 0.6 15 (20.0%)
7 A 2 A 9 (22.2%)
5 J 1 J 6 (16.6%)
Post-Application
(2 Weeks)
Bait 1.8 3: 1.1 5.6 d: 1.7 37 (75.6%)
4A 18A 22 (81.8%)
5 J 10 J 15 (66.6%)
No Bait 5.4 i: 2.5 0.2 3: 0.2 28 (3.5%)
10 A l A 11 (9.0%)
17 J OJ 17 (0.0%)
Sham Bait 5.6 :t 1.4 0.4 i 0.2 30 (6.6%)
16A 2A 18(1l.l%)
12 J 0 J 12 (0.0%)

 

* NC = Not counted, but dead snails were removed from study area.
'1‘ A = Total Adult C. nemoralis; I J = Total Juvenile C. nemoralis.

104

Table 5.2. The mean :1: SE temperature (°C) relative humidity (%) in each of the 5

blocks per week of treatment in SC 2005.

 

 

Block
Physical Block A Block B Block C Block D Block E
Parameter
Week One

Temperature 29.2 :1: 0.36 26.1 i 0.69 24.8 i 0.17 25.1 d: 0.17 26.4 :t 0.34

V W W9 X W, X, y W, X, y
Relative 82.7 i 0.69 92.7 i 3.1 95.8 :1: 0.92 87.3 i 1.6 84.2 i 2.2
Humidity v w, x w, y v, w, x, y, 2 v, w, x, 2

Week Two

Temperature 32.2 :L- 1.5 29.8 :1: 0.12 27.0 :t 1.4 26.9 :t 0.78 27.5 i 0.27

v v, w w w v, w
Relative 62.5 :1: 5.3 73.2 :t 3.6 76.0 d: 8.2 70.9 :1: 3.9 72.0 i 1.9
Humidity v v v v v

 

A lack of significant difference (Tukey’s Test, p > 0.05) between pairs in a single row is
indicated by shared letters.

105

Numberoflive snails

 

 

 

 

 

 

 

 

 

 

 

 

 

l6 4
l4 *
l2 1
10 1 ;
31. T“ ' r
6 1| 1"“ ‘1 3': i e’

' “5 1 .; a.
0 1 {mi-:31 55.40 4 n3

bait (12.4: 3.6) no bait (11.6 i 3.1) sham bait (8.8 i 1.6)
Block (mean i SE)

Figure 5.1. The mean (i SE) number of live snails found per block before application of
rmlluscicide.

106

CHAPTER 6: GENERAL CONLUSIONS AND RECOMMENDATIONS
General Conclusions

In Europe, where this species is native, the natural dispersal is much less when
compared to its dispersal in Michigan. This finding indicates that perhaps this species
disperses greater distances when playing the exotic role. However, this hypothesis was
not tested and remains open for exploration. The mark and recapture techniques used in
Europe were inaccurate due to the low recapture rates. However, recapture rates using
harmonic radar were much higher and the tracking was performed over shorter time
intervals. It cannot be stated that this species can disperse greater distance when it is
invasive, but it can be said that the European reports underestimated the dispersal
capabilities of this species. Therefore, if management agencies rely on dispersal
information that was acquired for this species in its native habitat it is plausible that the
rate of spread could be miscalculated. For example, Goodhart (1962) estimated that adult
C. nemoralis, in England, would not disperse more than 10.92 m in 4 years. The results
of the present study are drastically different. In the preferred woodland habitat adult C.
nemoralis were found to have a mean dispersal of 4.98 m/week (2004) and 2.1 m/day
(2004). There was also variation in the dispersal of individual C. nemoralis indicated by
the ‘big movers’ that could disperse distances of nearly 40 meters in less than two weeks.
Even though these ‘big movers’ were rare (Appendix G) their role in establishing a new
population could be important. This species is a hermaphrodite and capable of storing
sperm for long periods; an individual snail moving great distances could establish a new
population by itself.

Similar to the above mentioned observations, Baker (1988) reported that Theba

107

pisana dispersed greater distances when it was invasive. This snail species is native to
Western Europe and found from the Mediterranean to the United Kingdom. Cowie
(1984) reported on the dispersal of T. pisana from South Wales found this species moved
a maximum of 300 centimeters over a 100 day period. Cowie concluded that T. pisana
was a “sedentary” snail and showed a “reluctance to migrate”. In the 1920’s this species
was introduced to Australia and has become a very costly pest species (Baker, 2002).
Baker (1988) reported T. pisana in Australia moved greater than 55 meters in a single
month and greater than 75 meters in 3 months. The dispersal capabilities reported for T.
pisana in its native range and from areas where it is invasive are drastically different.
The data on T. pisana dispersal would indicate a snail species that is certainly not
“sedentary”. The mark and recapture techniques used by Baker (1988) were similar to
the techniques used in Europe. These techniques involved marking a large sample of
snails with paints, releasing them at a given starting point, and recapturing individuals
after some time interval (usually a month or greater).

Recently, Ozgo (2205a and 2005b) has hypothesized that habitat (primarily
temperature) is responsible for inter- and intrapopulation banding and color variation of
C. nemoralis. A strong association had been reported in the literature that indicated
banded and dark morphs prefer woodland habitats while the non-banded and light morphs
preferred grassland habitats (Cain and Currey, 1968; Jones et al., (1977); Ozgo (2005a
and 2005b). Ozgo, in Poland, demonstrated that habitat types are an important selection
force. This author hypothesized that banded individuals are more susceptible to over
heating in grassland habitats where the radiant energy is greater and the dark bands cause

the shell to absorb more solar radiation. Further, non-banded individuals are less likely to

108

overheat in grassland habitats due to the absence of dark shell pigmentation and lighter
overall shell color. In general open habitats are less humid and have higher temperatures
while shaded habitats are more humid and have lower temperatures (Ozgo, 2005a and
2005b). The association of a particular C. nemoralis morph to the environment was also
reported by Cain and Currey (1968). These authors found no five banded C. nemoralis in
the Marlborough Downs, England study site, however, they do mention an association
between dark shells and nettle patches (areas with dense vegetation) and light pink and
yellow shells found in grassland habitats. These authors reported that C. nemoralis had
much higher population densities (6 -— 10/m2) in the nettle patches than in the grassland
habitat (0.3 — 0.8/m2). The population density of C. nemoralis in Ingham County was
also higher in the woodland habitat (11.6 — 12.1/m2) than in the grassland habitat (0.0 —
0.05/m2).

Here in the US. the most commonly reported C. nemoralis morph is banded and
dark in color. This is true with the Ingham County population that was the focus of this
study. This morphological characteristic of C. nemoralis is a very important factor that
influences the natural short-distance dispersal of this snail. For C. nemoralis to disperse
naturally, under its own power, it must creep through its environment on a trail of mucus.
Mucus is costly for the snail to produce and is approximately 96 — 97% water (Denny,
1980). The more mucus a land gastropod produces the more water it will lose (Baur and
Baur, 1990; and Denny (1980)). Environments that maintain and keep moisture are more
suitable for snails because water is readily available and easily acquired. A woodland
habitat which offers a dense canopy and herbaceous layer is ideal for maintaining higher

moisture levels at the soil surface and promotes C. nemoralis dispersal. In Ingham

109

County, the surrounding habitats of the study site are grassland, open with little shade,
and tend to dry out during the summer months. Therefore, it may be difficult for this
population of C. nemoralis to naturally spread beyond the source woodland habitat. The
environmental conditions of the surrounding sink habitats are not suitable for this snail
species and may be acting as barriers preventing further dispersal. However, during
times of heavy rainfall (rain events lasting for several continuous days) the grassland
habitat does seem to maintain high enough moisture levels to support C. nemoralis
dispersal. One individual C. nemoralis moved nearly 40 meters in 11 days within the
grassland habitat. During this time rain events were frequent. This is an important
finding which demonstrated that natural barriers to dispersal may be breached if weather
conditions are favorable.

Cepaea nemoralis was first deliberately introduced to the US. 149 years ago. It
is not known how far this species has spread within the US. This is a result of a lack of
interest and research. Populations of C. nemoralis most likely go unnoticed and only
receive attention when they become a pest. The USDA-PPQ considers C. nemoralis to
be established and no eradication attempts will be conducted (Sullivan et al., 2004). An
established population is breeding and successfully creating offspring that can also
reproduce. There are several reasons that I feel this is not necessarily a good decision for
the USDA-PPQ to take. First, not enough information is known about how far this
species has spread and whether it is truly established. Established populations are those
that have individuals that are successfully reproducing. It may be that isolated
populations are established but it is not clear if the USDA-PPQ truly considers this

species established throughout the US. It is the opinion of this author that this species is

110

not broadly established and small isolated populations should be eradicated, if possible,
whenever they are found.

Second, no research has ever been conducted to investigate the impact C.
nemoralis has had on the native gastropod communities or native ecosystems in areas
where this species has been introduced. The data reported herein indicate that C.
nemoralis can live at high population densities as an exotic and has the potential to
dominate native gastropod communities. This species could have long lasting effects and
seriously impact native gastropods and perhaps drive local native populations to
extinction. This is a serious issue and should be researched further.

Third, C. nemoralis is known as a pest species in Europe. In the US. C.
nemoralis has only been labeled a pest from vineyards in New York (Martinson, 1999).
Cepaea nemoralis may appear to be benign throughout its non-native range, however this
current scenario could easily be changed. Grosholz (2005) documented a case where a
non-native bivalve in California, introduced 50 years ago, was thought of as benign and
having relatively no impact on the native ecosystem. However this non-native bivalve
quickly became a serious problem with the introduction of another non-native species of
marine crab. This phenomenon is called “invasional meltdown” and it suggests that an
ecosystem is more easily invaded with increasing numbers of exotic animals and that the
interaction between these exotics may allow them to become more invasive (Ricciardi,
2001). In the case presented by Grasholz the introduced crab began to eat native
bivalves, thus creating new niche opportunities for the relatively ‘quiet’ non-native
bivalve which has now allowed for the rapid spread of the non-native bivalve. It is likely

that another non-native species could be introduced allowing for C. nemoralis to utilize

lll

newly created niche opportunities and become a serious pest species here in the US.
The economic impact on agriculture could be serious if C. nemoralis became as
pestiferous here in the US. as it is in Europe.

Fourth, the dispersal capabilities of C. nemoralis in the US. are poorly
understood. This study is the first to quantify the short-distance dispersal of C. nemoralis
in a non-native environment. The abiotic (temperature and humidity) and biotic
(vegetation) conditions of the environment are very important for snail dispersal.
Knowing how snail dispersal is closely tied to these conditions will allow for better
recognition of source and sink habitats for invading snail species. Identifying sink
habitats will allow those agencies responsible for the management of invasive species to
evaluate the disruptive properties of natural barriers to snail dispersal. Corridors can also
be identified and potentially modified, if needed, to prevent further spread. Much more
research is warranted to determine the dispersal ecology of invasive land snails in a non-
native environment.

Every year more and more exotic snail species are identified coming into the US.
and little attention is paid to these invaders. Between 1999 and 2001 seven new species
of land snails were identified coming into the US. (Robinson and Slapcinsky, 2005).
Sullivan et al. (2004) reported that 12% of containers found at container yards in Detroit,
Michigan were infested with one or more species of exotic snail (Xerolenta obvia,

C andidula intersecta, Monacha cartusiana, and Hygromia cinctella). Cepaea nemoralis
was also found at several of these sites in Detroit but no attempt to eradicate them was
made because this species is considered established. The USDA-PPQ eradicated some of

the snails (X. obvia and M. carrusiana) found at these container yards. The USDA-PPQ

112

admits that exotic snails have been overlooked as a pest problem (Sullivan, 2004). They
also suggest that many exotic snails have become naturalized over the last 100 years with
minimal impact to agriculture. They further admit that “the biology of many snails is
poorly described and they may not be recognized as damaging pests (Sullivan, 2004)”.
This author feels that we should remain cautious and not become complacent with
regards to these “naturalized” exotic snails. Very little biological and ecological
information exists about many of these exotic snails in non-native ranges and we should
not assume them to be benign. We should also not look to find answers to the biological
and ecological questions we have about these exotic land snails in the literature regarding
them in there native ranges. As this current research has demonstrated that natural
history traits and dispersal ecology information may be different from native to non-
native ranges.

Exotic species have major economic and ecological impacts. Controlling and
managing them has become a serious problem in the US. Simberloff et al. (2005)
suggested that it is inadequate research and funding, insufficient policy, and gaps in
scientific knowledge that has lead to this problem in management and control. This rings
true for the exotic land snail dilemma as well. Cowie (2005) called for better quarantine
strategies, pre-entry regulations and screening, and establishing a rapid response to
eradicate new populations of invading land snails as a means to prevent establishment
and spread of an invader. Sullivan et al. (2004) however has stated that the USDA-PPQ
does attempt to prevent exotic snails from entering the US, but they do very little when
it comes to eradicating them. It seems that if a local population is deemed “established”

no eradication attempts will be made. I am concerned, however, with the policy that sets

113

the criteria for whether a population is established or not. There is a “hurry up and wait”
atmosphere when it comes to dealing with exotic land snails and doing nothing is
becoming the norm. The stand of the USDA-PPQ is that the invading land snail has to be
causing damage before eradication attempts are made (Sullivan et al., 2004).

It is the opinion of this author that the complacency and attitude of the USDA-
PPQ towards C. nemoralis may be regretted in the future. This research has shed light
upon the short-distance dispersal capabilities and population dynamics of C. nemoralis as
an exotic and invader. Cepaea nemoralis has the potential to become another example of
“what can go wrong” if the threat of an invading organism is overlooked. Lack of
knowledge and information on dispersal and natural history make research into C.
nemoralis and other invasive land snail species very important.
Recommendations

Land snail dispersal can be determined accurately using harmonic radar tracking
techniques. This new technique offers a high degree of accuracy without the labor
intensive mark-and-recapture methods traditionally used to estimate dispersal. Further
work needs to be done to determine the dispersal of non-banded exotic C. nemoralis in
grassland habitats. There have been reports of non-banded C. nemoralis populations in
New York. A comparative dispersal study using HR should be performed placing non-
banded C. nemoralis in woodland habitats and in grassland habitats. Further research
needs to be conducted in Europe to determine the dispersal capabilities of this species and
others using harmonic radar. This would allow for direct comparisons of dispersal
between this species in its native range to snails in North America. Understanding the

natural history and short—distance dispersal of any invasive land snail in more detail will

114

help with future control and eradication.

The example of Achatina fulica (See Chapter 1 for a review of A. fulica) has also
demonstrated that many of these exotic snails may be harboring organisms that can cause
disease in humans or wildlife. It is not known what parasitic organisms these introduced
land snails could be bringing into the US. No research is being conducted to monitor
and survey this potential threat to both humans and wildlife. There are examples in the
literature of introduced species harboring parasites that could infect native species.
Irizarry-Rovira et al. (2002) reported that a panther chameleon, F urcifer pardalis Cuvier,
1829, found in Indiana was infected with the microfilarial nematode, F oleyella sp.
Panther chameleons, and this species of nematode, are native to Madagascar and this
individual chameleon was imported to the US. through the pet trade. This particular
species of nematode can cause disease (thrombosis, edema, and necrosis) in reptiles and
the vector for this parasite is the mosquito (Culex sp. and Aedes sp.). Here in the US. we
have native species of mosquito that could serve as a vector for this parasite. It is easy to
see that an epizootic could have occurred in our native reptiles if this parasite had spread
via the mosquito vector. A serious threat exists from many of these exotic species
because they may carry infectious agents that could potentially lead to outbreaks of
disease in both human and wildlife populations. Snails (aquatic and land) and molluscs
in general serve a vital role in all digenetic trematode life cycles. Surveys should be
conducted to identify any parasites that these non-native snail species are harboring.

The population of C. nemoralis in Ingham County was most likely introduced
when green ash trees were planted by a commercial nursery. The Snail Central site was a

field before the trees were planted in the late 1980’s and early 1990’s. This particular

115

morph of C. nemoralis does not survive well and is unlikely to establish a population in
an open field. Therefore, it is probable that this population was introduced during the
time of tree planting. This demonstrates the importance of human activity in the
movement of this snail species throughout the country. This population has been at this
location for over 15 years and has not managed to spread beyond the study site. This is a
strong indicator that the surrounding areas are indeed sink habitats and act as barriers to
the short-distance dispersal of C. nemoralis. However, it is only a matter of time before
individuals are transported to far off places. Currently, SC has been put up for sale by the
landowners. It is likely that the property will be developed and houses will be built. It is
plausible that as this development takes place and the land is cleared that individual C.
nemoralis could be removed and transported to distant places. This type of long-distance
dispersal must be prevented and it is the recommendation of this author that this

population of C. nemoralis be eradicated.

116

Appendix A

117

Table A. 1. The types of plants identified from each of the 5 habitats found at the study

site in Ingham County, Michigan.

 

Plant Species Snail Blue South North Homestead
Central Spruce Field Field

Green Ash, Fraxinus X X
pennsylvanica

White Ash, Fraxinus
americana

Silver Maple, Acer
saccharinum

Domestic Apple, Malus
pumila

Trembling Aspen,
Populous tremuloides

Pin Oak, Quercus palustris

Honey Locust, Gleditsia
triacanthos

White Mulberry, Moms
alba

Blue Spruce, Picea
pungens

Staghom Sumac, Rhus
typhina

Poison Ivy, Rhus radicans
Common Dandelion,
Taraxacum oflicinale
Canada Golden Rod,
Solidago canadensis
Fleabane, Erigeron
canadensis

Curled Dock, Rumex
crispus

Common St. Johnswort,
Hypericum perforatum
Black Medick, Medicago X

lupulina

White Cockle, Silene X X
pratensis

Ox-eye Daisy, X X

C hyrsanthemum

Ieucanrhemum

Lamb's-Quarters, X X
C henopodium album

Sulphur Cinqefoil, X X X X
Potentilla recta

Milkweed, Asclepias X X
syriaca

Water Hemlock, Cicuta X

maculate

Chicory, Cichorium intybus X X

><><><><><><

><><><><><
><><><><><><><><><><><><
><>< ><><><><
><><><><

 

118

Table A.1. Continued

 

Plant Species Snail Blue South North Homestead
Central Spruce Field Field
Red Raspberry, Rubus X X X
idaeus
Honeysuckle, Lonr'cera sp. X
White Clover, Trifolium X X
repens
Grape, Vitis sp. X X X
Wild Carrot, Dancus X X X X
carom
Myrtle, Vinca minor X X
Lilac, Syringa vulgaris X
Peony, Paeom'a sp. X
Common plantain, X X X X X
Plantago major
Smooth Brome, Bromus X X X X
intermis
Giant Foxtail, Setaria X X X X
faberi
Various Grasses (Poacaea) X
Moss (BryOPhyta) X X X X

 

ll9

Appendix B

120

Nonh

West East

225'

 

South

Figure B]. Compass designations for determining directionality in C. nemoralis

dispersal from the SC and SF in Ingham County, Michigan.

121

Appendix C

122

Table C. l. TAG designation, transponder type, shell diameter (mm), age, and habitat

release site for individual C. nemoralis tracked in 2003.

 

 

TAG Transponder Shell Diameter Age Habitat
Designation Type (mm)
X1 Monopole 22 Adult SC
X2 Monopole 2 1 Adult SC
X3 Monopole 2 1 Adult SC
X4 Monopole 22 Adult SC
X5 Dipole 20 Adult SC
X6 Monopole 20 Adult SC
X7 Monopole 2 1 Adult SC
X8 Monopole 2 1 Adult SC
X9 Monopole 20 Adult SC
X1 0 Monopole 2 1 Adult SC
X1 1 Monopole 21 Adult SC
X1 2 Monopole 20 Adult SC
X 1 3 Monopole 2 1 Adult SC
X14 Monopole 22 Adult SC
Y1 Monopole 19 Juvenile SC
Y2 Monopole 1 7 Juvenile SC

B9 Monopole 1 5 Juvenile SC

123

Appendix D

124

Table D. 1. TAG designation, transponder type, shell diameter (m), age, and habitat

release site for individual C. nemoralis tracked in 2004.

 

 

TAG Transponder Shell Diameter Age Habitat
Designation Type (mm)
Z1 Dipole 23 Adult SC
Z2 Dipole 24 Adult SC
Z3 Dipole 22 Adult SC
Z4 Dipole 22 Adult SC
Z5 Dipole 23 Adult SC
Z6 Monopole 23 Adult SC
Z7 Monopole 2 1 Adult SC
Z8 Monopole 22 Adult SC
Z9 Monopole 22 Adult SC
210 Monopole 23 Adult SC
F 1 Monopole 23 Adult SF
F2 Monopole 23 Adult SF
F3 Dipole 23 Adult SF
F4 Dipole 23 Adult SF
F5 Monopole 22 Adult SF
F 6 Monopole 22 Adult SF
F 7 Dipole 22 Adult SF
F8 Monopole 23 Adult SF
F9 Monopole 21 Adult SF

F 10 Monopole 22 Adult SF

125

Appendix E

126

Table E.1. TAG designation, transponder type, shell diameter (m), age, and habitat

release site for individual C. nemoralis tracked in 2005.

 

 

TAG Transponder Shell Diameter Age Habitat
Designation Type (mm)
B l Monopole 20 Adult SC
B2 Monopole 2 1 Adult SC
B3 Monopole 20 Adult SC
B4 Monopole 20 Adult SC
B5 Monopole 2 1 Adult SC
B6 Monopole 20 Adult SC
B7 Monopole 2 1 Adult SC
B8 Monopole 2 1 Adult SC
B9 Monopole 20 Adult SC
B 1 0 Monopole 20 Adult SC
M1 Monopole 20 Adult SF
M2 Monopole 20 Adult SF
M3 Monopole 20 Adult SF
M4 Monopole 22 Adult SF
M5 Monopole 20 Adult SF
M6 Monopole 2 1 Adult SF
M7 Monopole 2 1 Adult SF
M8 Monopole 2 1 Adult SF
M9 Monopole 2 1 Adult SF

M10 Monopole 20 Adult SF

127

Appendix F

128

Table F .1. The 33 sites that were surveyed for the presence of C. nemoralis from

Ingham County, Michigan in 2003 - 2005.

 

 

Number Location Name Coordinates Number of C epaea
nemoralis present
1 Hunt’s Verge T.3N.-R.1W section 2
29 SW/SW
2 Hunt’s Yard T.3N.-R.1W section 0
29 SW/SW
3 Hunt’s Lane T.3N.-R.1W section 0
29 SE/SW
4 Hunt’s Pond 42°36.790’N — 0
84°27.168’W
5 Hunt’s Property, North of T.3N.-R.1W section 0
Harper Rd. 29 SW/SE
6 Hagadom Rd. 1 Verge T.3N.-R.1W section 0
29 NW/NW
7 Hagadom Rd. 2 Verge T.3N.-R.1W section 0
29 SE/SW
8 NW Comer of Hagadom and T.3N.-R.1W section 0
Harper Rds. 29 SE/SW
9 Mud Creek and Lamb Rd., NW T.3N.-R.IW section 0
Comer 20 SW/SW
10 Mud Creek and Lamb Rd., NE T.3N.-R.1W section 0
Comer 29 SW/SE
l 1 Discount Trees, NW Comer of 42°36.788’N - 0
Okemos and Harper Rds. 84°25.995’W
12 Discount Trees, Main Office T.3N.-R.1W section 0
20 SW/NW
13 Discount Trees, NW Comer of T.3N.-R.1 W section 0
Darling Rd. 20 SE/NW
14 Discount Trees, North of T.3N.-R.1W section 0
Harper Rd. 30 SW/SE
15 Collar’s Field, North of Study T.3N.-R.1W section 0
Site 29 SW/SW
l6 Collar’s Field, West of Study T.3N.-R.1W section 0
Site 29 SW/SW
17 Collar’s Woods, West of Study T.3N.-R.1W section 0
Site 29 SW/SW
18 Collar’s Property, North of T.3N.-R.1W section 0
Harper Rd. 29 SW/SW
19 Harper Rd. Verge, South of T.3N.-R.1W section 0
Study Site 32 NW/NW
20 NE Comer of Rail Road Tracks T.3N.-R.1W section 0
and Harper Rd. 30 SE/SE
21 SE Comer of Rail Road Tracks T.3N.-R.1W section 0
and Harper Rd. 32 NW/NW
22 Field West of Rail Road T.3N.-R.1W section 0
Tracks, South of Harper Rd. 32 SW/NW
23 Woods East of Rail Road T.3N.-R.lW section 0
Tracks, South of Harper Rd. 32 SW/NW
24 Field NE of Rail Road Tracks, T.3N.-R.lW section 0
North of Harper Rd. 30 NW/SE

 

129

 

Table F.l. Continued

 

 

Number Location Name Coordinates Number of C epaea
nemoralis present

25 NE Comer of Sycamore Creek T.3N.-R. l W section 0
and Harper Rd. 30 SE/SE

26 NW Corner of Sycamore Creek T.3N.-R.1W section 0
and Harper Rd. 30 SW/SE

27 SW Comer of Sycamore Creek T.3N.-R.1W section 0
and Harper Rd. 31 NE/NE

28 SE Comer of Sycamore Creek T.3N.-R.1W section 0
and Harper Rd. 31 NE/N E

29 Seiler’s Grape Vines and Apple T.3N.-R. l W section 0
Trees 32 SWINE

30 Woodlot, Ingham lnterrnediate T.3N.-R.1W section 0
School District 32 SE/SW

31 Treemont Manor, Hagadom T.3N.-R.1W section 0
Rd. 20 SE/SW

32 Kranz Property T.3N.-R.1W section 0
19 NEWS

33 Atkinson Property 42°38.8’N - 0
84°24.1’W

 

130

Appendix G

131

.o
O
.1

 

99¢???
w-bMO‘flOO

Frequency

 

99
-—'l\)

 

O

0

0 4 7 _\.

m I I ~ \ \ /
ere, 3'90) 69% [0'90] 10'”?

etc/5' (5,3, 610’s ’3‘

Dispersal (meters)

Figure 0.1. Frequncy histogram ofC. nemoralis daily dispersal from SC in 2004.

132

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

I l

1 "X ll
° ‘3.9 9 0. 9 029
026,913 mete/3' mete/5' refs

Dispersal (meters)

Figure (12. Frequncy histogram of C. nemoralis daily dispersal from SF in 2004.

133

 

 

 

 

 

 

 

Frequency
O
b.)

.o
N

 

 

 

 

 

 

 

 

 

 

 

 

0.1 . E
0 ‘3 T, I 1'. '= l- ] E----

 

0 0 4 7 A
02 -l - ~ ~ I
ever 3.90) 6.9% 10.90) 112%
8,013 [015' 6,613. ’3
Dispersal (meters)

Figure 0.3. Frequncy histogram of C. nemoralis weekly dispersal from SC in 2004.

134

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

0 E"; - *1 J V" = T r—‘l fl L
7

0 4 A
re, 3 9 .9 026% 0. 9 02%,}

0101513, 0701613

Dispersal (meters)

Figure (14. Frequncy histogram of C. nemoralis weekly dispersal fiom SF in 2004.

135

Freq

 

 

 

 

 

 

 

o 0,

 

029,0]:

Dispersal (meters)

Figure 6.5. Frequncy histogram ofC. nemoralis daily dispersal from SC in 2005.

136

C 4‘ \
’3‘

0.8
0.7
0.6

3; 0.5 "

= .

“5 0-4l

3

E 0.3 1
0.2 +

.__L

__l__J_____J

 

 

 

Dispersal (meters)

Figure 0.6. Frequncy histogram of C. nemoralis daily dispersal from SF in 2005.

137

Appendix H

138

 

 

1 meter

 

 

 

Figure H.1. Daily dispersal of snail 21 over a 14 day period from
SC in 2004.

139

 

1 meter

 

 

 

Figure 11.2. Daily dispersal of snail ZZ over a 14 day period from
SC in 2004.

I40

 

1 meter

 

 

 

Figure H.3. Daily dispersal of snail Z3 over a 14 day period from
SC in 2004. *

l4]

 

1 meter

 

 

 

Figure HA. Daily dispersal of snail Z4 over a 14 day period from
SC in 2004. '

142

 

1 meter

 

 

 

Figure H.5. Daily dispersal of snail Z5 over a 14 day period from
SC in 2004. -

143

 

1 meter

 

 

 

Figure H.6. Daily dispersal of snail Z6 over a 14 day period from
SC in 2004.

144

 

1 meter

 

 

 

Figure H.7. Daily dispersal of snail Z7 over a 14 day period from
SC in 2004.

I45

 

1 meter

 

 

 

Figure H.8. Daily dispersal of snail Z8 over a 14 day period from
SC in 2004. -

I46

 

1 meter

 

 

 

Figure H.9. Daily dispersal of snail Z9 over a 14 day period from
SC in 2004.

I47

 

1 meter

 

 

 

Figure H.10. Daily dispersal of snail Z10 over a 14 day period from
SC in 2004. ‘

148

 

1 meter

 

 

 

Figure H.11. Daily dispersal of snail Bl over a 14 day period from
SC in 2004. -

149

 

1 meter

 

 

 

Figure H.12. Daily dispersal of snail 82 over a 14 day period from
SC in 2004.

150

 

1 meter

 

1

Figure H.13. Daily dispersal of snail B3 over a 14 day period from
SC in 2004.

 

 

151

 

1 meter

 

 

1

Figure H.14. Daily dispersal of snail B4 over a 14 day period from
SC in 2004. -

 

152

 

1 meter

 

 

 

Figure H.15. Daily dispersal of snail B5 over a 14 day period from
SC in 2004. -

153

 

1 meter

 

 

 

Figure H.16. Daily dispersal of snail B6 over a 14 day period from
SC in 2004.

154

 

1 meter

 

 

 

Figure H.17. Daily dispersal of snail B7 over a 14 day period from
SC in 2004.

155

 

1 meter

 

 

 

Figure 11.18. Daily dispersal of snail B8 over a 14 day period from
SC in 2004. '

156

 

1 meter

 

 

 

Figure H.19. Daily dispersal of snail B9 over a 14 day period from
SC in 2004.

157

 

1 meter

 

 

 

Figure H.20. Daily dispersal of snail B10 over a 14 day period from
SC in 2004.

158

Appendix I

159

 

 

 

 

Sham Bait

 

 

 

 

Figure 1.1. Design of the short-term experimental study. The five blocks are labeled A,
B, C, D, and E and each contains three treatment plots that were 10 x 10 meter in size
with a 3 x 3 meter sub-plot (treatment zone) located in the center. The three treatments

were bait, no bait and sham bait.

160

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