Illinois Digital Archives
Snails have a complex system of organs. The mouth contains a radula, a flexible, rib-bonlike
structure lined with rows of teeth, used to scrape food. On the snail’s head are
tentacles, which serve as chemosensory structures. Most snails in Illinois have an eye
at the tip of each upper tentacle. All internal organs are contained within the mantle,
inside the shell. Food travels through a digestive system consisting of a stomach, di-gestive
gland and intestine.The circulatory systemis semi-closed and has a heart with one
ventricle and one auricle. Breathing is accomplished by drawing air through the
pneumostome, a small opening in the mantle. Gas exchange occurs within the
A snail’s shell develops in the egg along with the rest of its body and continues to
grow until the snail reaches sexual maturity.The shell is formed by deposits of calcium
laid down by the mantle. As the shell grows in its coiled shape, whorls are added. A
snail cannot leave its shell. It has a strong muscle inside that is firmly attached to the
shell. Snail shells grow in a variety of shapes, including discoid, conical and beehive.
Shell shape, number and type of whorls and shell ornamentation, such as ribs or hairs,
aid in identification of species. Some snails have denticles, or “teeth,” that protrude
towards the center of the shell opening to prevent insect predators from entering and
eating the snail. Snail shells may persist long after the snail has died and often can be
used to identify species. Slugs have either a much reduced shell, located under the
mantle on the dorsal side, or no shell.
Most land snails are hermaphrodites, possessing both male and female sex organs
and gametes. When snails mate, fertilization often occurs in both individuals, and
both lay a clutch of from one to at least 20 eggs. Clutch number varies by species.
Generally, the larger the snail, the more eggs it will lay. Snails lay their eggs in spring
and fall. Eggs are deposited in a cool, damp place, often just under the soil’s surface.
The adult snail provides no care for the eggs. Hatching takes place in about seven to
10 days. The young snails emerge and begin to search for food immediately. Young
slugs have the same appearance as the adults, while young snails have one body whorl
Several adaptations help snails to survive. A snail’s skin contains glands that produce
mucus. The mucus prevents the snail from drying out and also helps it move. Dur-ing
very hot, dry weather and during very cold periods, snails and slugs may become
inactive. When a snail aestivates (hot weather) or hibernates (cold weather), it pro-duces
a thick mucus membrane over the opening of the shell to prevent further des-iccation.
Homing tendencies help snails to return to the same sheltered area after
activities, reducing the risk of traveling to a potentially dangerous habitat.
Most Illinois land snails are detritivores, eating decaying vegetation, such as leaves.
Some snails are carnivores, feeding on other snails or carrion. In Illinois, the gray-foot
lancetooth snail (Haplotrema concavum) eats other land snails. It has a thin, elongated
“neck” that it inserts into the shell of other snails. Its special barbed teeth then attack
the flesh of the prey snail.
Snails need to seek sheltered places to live, eat and rest. They prefer to live in moist
areas and are commonly found under logs, loose bark or coarse woody debris, and in
leaf litter on the forest floor. In general, snail populations are greatest in areas that
have high soil calcium levels. Calcium is needed by snails to produce the shell and to
regulate body functions.
Land snails move by gliding on a large, muscular foot. The muscles in the foot con-tract
in waves in the same direction that the animal is moving. Each wave allows the
muscles to grip the substrate and pull the snail forward. Glands in the foot produce
mucus to help the snail move along. Snails do move very slowly. One snail was
recorded to be moving at 0.0023 mph.
Snails are a food source for many animals. Some insects eat land snails. Firefly larvae
feed almost exclusively on snails. Land snails are an essential part of the diet of many
birds. During periods of egg-laying, female birds that normally eat snails increase their
snail consumption. The calcium in snail shells is a nutrient vital to embryonic devel-opment
and egg shell production in birds.
Anatomy Life History
Although there is little information available about snails and slugs, several institutions
in Illinois maintain research collections. The Field Museum of Natural History and the
Peggy Notebaert NatureMuseum, both in Chicago, and the Illinois NaturalHistory Sur-vey
in Champaign, have significant collections and conduct studies. Other organizations,
such as the U.S. Fish and Wildlife Service and the Illinois Department of Natural Re-sources,
support research of these species. The IllinoisWildlife Preservation Fund, com-prised
of taxpayer donations, helps to support further understanding of these creatures
by providing grants for projects, such as the development of this poster. Publications
about mollusks and other topics can be ordered through the order form at
Illinois Department of Natural Resources
Division of Education
One Natural ResourcesWay
Springfield, IL 62702-1271
Equal opportunity to participate in programs of the Illinois Department of Natural Resources (IDNR) and those funded by the U.S. Fish andWildlife Service and
other agencies is available to all individuals regardless of race, sex, national origin, disability, age, religion or other non-merit factors. If you believe you have
been discriminated against, contact the funding source’s civil rights office and/or the Equal Employment Opportunity Officer, IDNR,One Natural ResourcesWay,
Springfield, IL 62702-1271; 217/785-0067; TTY 217/782-9175.This information may be provided in an alternative format if required. Contact the DNR Clearing-house
at 217/782-7498 for assistance.
Printed by the Authority of the State of Illinois.
10M – 3/09 • IOCI 0759-09
Illinois Land Snails and Slugs © 2009, Illinois Department of Natural Resources
aestivation period of inactivity and reduced metabolism in summer or other
times of the year when temperatures are high enough to be
stressful to an organism
auricle a chamber of the heart that receives blood from the veins
carnivore animal that preys upon and eats other animals
chiton also called sea cradle, this mollusk lives on rocks in the ocean
and has a shell made of hard, overlapping plates
denticle a small, toothlike projection
detritivore an organism that eats dead plant or animal materials
discoid having a flat, circular shape, like a discus
dorsal the back or upper side of an animal
hermaphrodite organism possessing both male and female reproductive organs
hibernation period of inactivity in winter during which an organism has
reduced metabolic functions
mantle the part of a mollusk that surrounds the organs and lines and
secretes the shell
mucus a thick fluid secreted by mollusks that assists them in movement
and protection; helps prevent the body from drying out
pneumostome an opening in the mantle of a gastropod where air can enter for
radula a flexible band lined with rows of small teeth in the mouth of
gastropods; used to scrape food
scaphopod a burrowing, marine mollusk with a long, tapering shell
tentacle an elongated, unsegmented extension from a snail’s head used
for sensory purposes
ventral belly or lower side of an animal
ventricle lower chamber of the heart; receives blood from the auricle and
pumps it to the snail’s tissues
whorl one of the turns of a spiral shell
In today's world of rapid environmental changes, land snail populations are susceptible
to decline. Snails are particularly affected in areas where acid rain is prevalent.The acidic
soil contains less-than-normal amounts of available calcium that snails need for proper
growth and life functions. A research study in Europe documented reduced populations
of certain types of forest-dwelling birds attributed to reduced populations of their main
food source, land snails. Acidic rainfall led to the decline in snails, and the decline in the
bird populations followed.Other threats to snails include habitat loss due to agricultural
use or construction and the application of salts and chemicals to roads in the winter. It
is believed that forest fires and floods can be detrimental to populations of land snails, too.
Unfortunately, some snail species living in North America are not native. These nonna-tive
species are mainly from Europe, arriving in shipments of food or plants and escap-ing
to establish populations. Some do little damage, but others, such as the giant
gardenslug (Limax maximus) can damage crops and compete with native land snails for
resources. Any animal or plant that is not native to an area can upset the natural balance
of the ecosystem.
Because land snails are not sufficiently studied, it is difficult for conservation specialists
to assess the measures needed to protect them. You can help to conserve land snails,
though. Learn to identify the snails in your area. Snails can be found in many habitats,
even a small back yard. Look under rocks, logs and in leaf litter. Keep records of the snails
you find.Write down the name of the snail, the date you observed it, precisely where you
found it and in what type of habitat it was found (woods, wetland, urban, etc.). Take a
photograph, if you can. Put the snail back where you found it and return any logs and
rocks to their original position.Note any trends in your observations and report themto
scientists in your area. Allow part of your property to remain natural with fallen logs and
leaf litter to provide snail habitat. Join a shell club or malacological society, such as the
Chicago Shell Club or the Conchologists of America.
Measurements indicate largest shell
dimension for snails and longest body
length for slugs.
Appalachian pillar Cochlicopamorseana (Doherty,
1878) – 1/4 inch – This glossy, spindle-shaped
snail is found in and around rotting logs and leaf
armed snaggletooth Gastrocopta armifera (Say,
1821) – 1/8 inch – The shell of this snail has
projections, called teeth or denticles, in its aper-ture
that help protect its soft body from being
eaten by insect predators.
bladetooth wedge Xolotrema fosteri (F. C. Baker,
1921) – 5/8 inch – The bladetooth wedge is
named for its prominent denticle, or toothlike
structure, on the parietal surface of its shell. It is
one of themost common land snails in the state.
brittle buttonMesomphix friabilis (W.G. Binney,
1857) – 7/8 inch – This shiny snail frequents
moist woodlands. It has a blue-tinged body and
a somewhat flexible, translucent shell.
broad-banded forestsnail Allogona profunda (Say,
1821) – 1 inch – The broad-banded forestsnail
once lived in Illinois because shells of this species
are present. Populations exist in neighboring
states, so it is possible that the species may still
bronze pinecone Strobilops aeneus Pilsbry, 1926
– 1/8 inch – Raised ribs are a recognizable trait
of the bronze pinecone's shell. In the shell's in-terior,
there are also raised ridges, called lamellae.
The lamellae may serve as stabilizing structures
when the snail is in motion.
Carolina mantleslug Philomycus carolinianus
(Bosc, 1802) – 2 inches – The Carolina
mantleslug is one of Illinois' native slugs. It
prefers moist, deciduous woodland habitats and
does not invade gardens. When disturbed, it
emits very sticky mucus to detract predators.
carinate pillsnail Euchemotrema hubrichti (Pilsbry,
1940) – 3/8 inch – Empty shells from the grace-ful,
lens- or flying saucer-shaped snail, the cari-nate
pillsnail were discovered in Illinois in 1939.
Several small populations of living individu-als
were later discovered on limestone bluffs
in southern Illinois, the only place on earth
cherrystone dropHendersonia occulta (Say, 1831)
– 1/4 inch – The cherrystone drop is rarely
found in Illinois. It has a thick shell and an op-erculum,
or a hard, flexible covering, that pro-tects
the soft body when the animal is withdrawn
into its shell.
compound coilHelicodiscus parallelus (Say, 1817)
– 1/8 inch – The compound coil looks like a
neatly wound coiled rope. It occurs widely across
Illinois in leaf litter and near human habitations.
depressed ambersnail Oxyloma peoriense (Wolf,
1894) – 3/8 inch – Named for Peoria, Illinois,
the locality fromwhere it was first described, this
snail is known from only a small number of lo-cations
in the state. It has a distinctive oval shape
and flexible shell.
domed supercoil Paravitrea significans (Bland,
1866) – 3/16 inch – Translucent and shiny, the
domed supercoil has a distinctly shaped, sloping
aperture and a tightly coiled, dome-shaped shell.
dusky arion Arion subfuscus (Draparnaud, 1805)
– 3 inches –This slug is introduced fromEurope.
It generally lives around human habitations and
can be a garden pest.
globose dome Ventridens ligera (Say, 1821) – 1/2
inch – The globose dome tolerates a wide range
of habitats over the state, including areas dis-turbed
gray fieldslug Deroceras reticulatum (Müller,
1774) – 2 inches –The gray fieldslug, believed to
have originated in western Europe, has success-fully
invadedmany areas of the world. It can be-come
a garden pest. This animal emits
milky-whitemucus when disturbed and can self-amputate
its tail when threatened.
gray-foot lancetooth Haplotrema concavum (Say,
1821) – 3/4 inch – A voracious predatory snail,
the gray-foot lancetooth has a specially adapted
radula with barbed toothlike projections that
enable it to eat the flesh of other snails. Its elon-gated
neck region permits it to extend into the
shell of its helpless victim. It is the only predatory
land snail in Illinois.
ice thorn Carychium exile I. Lea, 1842 – 1/16
inch – This tiny snail has a translucent, white-tinged
shell and lives in moist leaf litter, some-times
in great numbers. It is fairly common in
Illinois deciduous woodlands.
Iowa Pleistocene snail Discus macclintocki (F. C.
Baker, 1928) – 1/4 inch – Once believed to be
extinct, living populations of this snail were dis-covered
in 1955. It occurs in very limited areas
in northwestern Illinois.This glacial relict species
was fairly common in a large area south of the ice
during the last Ice Age, but as the climate
warmed, most of the individuals died. Those
that survived live in areas that remain cool year
round. The Iowa Pleistocene snail is a federally
Roger's snaggletooth Gastrocopta rogersensis
Nekola and Coles, 2001 – 1/10 inch – Roger’s
snaggletooth is the most recently discovered
and named snail species in Illinois. It lives on
limestone bluffs in a few places along the
small spot Punctum minutissimum (I. Lea, 1841)
– less than 1/16 inch – Aptly named, the small
spot is about the size of the period at the end of
this sentence. It is one of the smallest land snails
in Illinois.While it is not as easily found as larger
snails, it is abundant in leaf litter.
striped whitelip Webbhelix multilineata (Say,
1821) – 1 inch – This multiply striped snail
occupies wet habitats, such as near swamps and
on river banks.
thin-lip vallonia Vallonia perspectiva Sterki, 1893
– 1/16 inch – A tiny, white snail with a ribbed
sculpture, the thin-lip vallonia lives in openings
in woods or in fields.
tigersnail Anguispira alternata (Say, 1816) – 7/8
inch – A common snail, this species is easily rec-ognized
by the vivid rust-colored markings on
its shell. It is often found in large numbers.
toothed globeMesodon zaletus (A. Binney, 1837)
– 1 inch – This large, round snail is widely dis-tributed
in Illinois and is common in hardwood
forests. Its shell has a broadly reflected lip, or
outer edge of the opening, and a denticle on the
whitewashed rabdotus Rabdotus dealbatus (Say,
1821) – 1/2 inch – This species was recorded in
the first half of the 20th century in Illinois but
has not been observed alive in the state since
then. Southern Illinois is at the northernmost
boundary of its range, and it is questionable as to
whether this species is still living in the state.
I l l i n o i s
Snails & Slugs
The snail species shown in this photograph occur in Illinois. Photo © 2008,Marla L. Coppolino.
External snail anatomy
Photo © 2008, Marla L.Coppolino
Illustrations by Marla L.Coppolino
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