Can Snails Live Outside Their Shell? Can They Bite? Test Your Knowledge of These Under-Appreciated Slime Producers
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Land Snails in Illinois Can snails live outside their shell? Can they bite? Test your knowledge of these under-appreciated slime producers. Story and Photos ilently and slowly gliding in Very remarkable is their great variety of the damp, hidden nooks are sizes and shapes. Snail shells can be coni - By Marla Coppolino some lowly yet important cal in form to very flat and disc-shaped. Mesodon zaletus members of Illinois’ natural The shell of the largest species measures toothed globe,, shell width 1 inch habitats: the land snails. more than an inch in width, while the tini - Land snails, which est is less than 1/16th inch across. include slugs, are one of the Smost understudied groups of animals, Named for the toothlike structure on but they are certainly deserving of our the shell, the bladetooth wedge is one of attention. Often bearing the reputation the most common land snails in Illinois. as mere pests, Illinois’ native land snails play Xolotrema fosteri an essential role in the bladetooth wedge,, shell width 5/8 inch functioning of its ecosystems. Approxi - mately 124 species are currently known to inhabit the state’s The toothed globe snail (also top of forests and grasslands, page) is widely distributed in Illinois with more than 70 per - and common in hardwood forests. cent of species occupy - ing wooded habitats in southern Illinois. 8 / Outdoor Illinois June 2009 ) . n o s n h o J c i r E Euchemotrema hubrichti y b o carinate pillsnail,, shell width 3/8 inch t o h P ( Also notable is that the majority of Previously believed to be extinct, the Illinois’ species are quite small—less only place in the world that the carinate Mesomphix friablis than 1/4 inch in shell width—and most brittle button,, shell width 7/8 inch pillsnail (above) is known to exist is of these inhabit the leaf litter of forest - ed areas. They might be hard to detect some limestone bluffs in southern But for land snails, the shell also offers by the unaided (and unknowing) Illinois. Found in moist woodlands, the protection from desiccation, the most human eye, but they exist, and are brittle button (right) has a blue-tinged serious threat to terrestrial existence. doing their jobs very well. body and translucent shell. The snail can withdraw its body far into Land snails and slugs are members of the shell, and remain inactive for long the class Gastropoda, meaning “stom - invertebrate animals including clams, periods of time when it is hot and dry ach-foot,” because they move upon a mussels, limpets, chitons, tusk shells, or in freezing temperatures. large, muscular ventral surface called a octopuses and squid. Land snails are spe - One common misconception about foot. The animal’s internal organs, cial in that they evolved from aquatic land snails is that they can “crawl away” which include a digestive gland, lung, ancestors and possess many unique adap - from their shells. This is not possible heart and reproductive organs, are tations to survive in terrestrial habitats. because the snail is attached to its shell located within the mantle cavity, inside and it would survive for only a short the shell of the animal. In the case of The Shell time if removed. Only when a snail dies slugs, the organs are just behind the Snails are easily recognizable animals does it leave behind an empty shell. head region. because of their distinctive shells. Like The shell is present from the time Gastropods include both land and those of their aquatic relatives, the land the snail develops as an embryo. As a aquatic snails, and are members of the snails’ shells offer protection from hatchling, it is thin and flexible, and has phylum Mollusca, a diverse array of predators for the soft-bodied animal. only about one whorl (a 360 degree coil from the center). As snails eat and grow, the shell thickens and additional coils form around the central axis. In adults of some species, projections grow with - in the aperture (the opening of the shell), which, when withdrawn into its shell, help protect the snail from preda - tors. The projections are thought to help stabilize the weight of the shell when the snail is actively moving about. Slugs are snails, too, but have evolved to not require the full shell of The vivid, rust-color marking on the tigersnail make it easy to identify this Anguispira alternata common snail. tigersnail,, shell width 7/8 inch June 2009 Outdoor Illinois / 9 their shelled relatives. Philomycus carolinanus Found in moist, decidu - self-fertilizing, most seek a mate with Many slugs actually do Carolina mantleslug,, body length 2 in.. ous woodland habitats, which they exchange sperm to fertilize have a small bit of shell the partner’s eggs. Eggs are deposited the Carolina mantleslug remaining under the in soil, or under logs or woody debris surface of their skin, does not invade gardens. and then abandoned. Depending on the over the mantle area, species, embryos develop and hatch in but it does little to pro - mucus, is an impor - one to a few weeks, emerging as small tect the animal. tant adaptive mecha - snails with just one whorl of shell. Juve - Instead, slugs have nism to help the snail nile snails begin to feed immediately. evolved other means of survive. Its body and staying hydrated and foot have mucous Feeding protected. For one, glands, which secrete Most land snails are generalist herbi - their bodies produce the mucus as it moves. vores, consuming the detritus (decom - more mucus than most The mucus makes it posing plant material) of their environ - shelled snails do, and it easier for snails to ment. They also are known to consume often is quite thick and glide over any surface, soil directly and some fungi. resists evaporation. Some slugs curl up even if rough or sharp. In fact, a snail Snails eat by means of a structure in when provoked, while others writhe can even crawl over the edge of a the mouth called the radula, a chitinous and secrete other chemicals that taste razor blade without getting cut. (similar to fingernail tissue) ribbon offensive to predators. Another benefit of mucous trails is bearing fine teeth, with which it rasps that snails can sense and follow them, off bits of food. Slime allowing them to follow other snails to A few snail species in Illinois are car - Snails exude a slime trail, visible as areas of food or for breeding. Like a nivorous, either in part or as specialists. a silvery path on the surface after homing mecha - Haplotrema con - they’ve crawled over it. Slime, or nism, the trails Haplotrema concavum cavum , the gray- gray-footed lancetooth snail,, shell width 3/4 inch prevent snails footed lancetooth from wandering snail, feeds upon Land snails glide on a large, muscular foot off the known other land snails. that contracts in waves in the direction paths of safety. Its radula is spe - the animal is moving. Glands in the foot cially adapted produce mucus that aids in movement. Senses with barb-like Snails’ bodies teeth, which have well-devel - enable it to tear Mesodon zaletus toothed globe,, shell width 1 inch oped tactile the flesh of other responses, one of snails. With this the most important adaptations for soft- elongated “neck,” it crawls inside the bodied animals. With one touch of your shell of its prey as it tries—unsuccess - finger, most will quickly retreat into fully—to withdraw from the lance - their shells. tooth. In addition to its carnivorous Two pairs of tentacles (often mistak - feeding abilities, these snails locate enly called “antennae”) on the snail’s their prey by following mucous trails. head contain chemoreceptors at their tips. The longer pair also usually bears Land Snail Ecology eye spots that don’t form images but What makes land snails so important are capable of detecting changes in to Illinois’ ecosystems? light. The lower pair is shorter, and Snails serve an essential role in the used primarily for chemoreception, breakdown of plant material because guiding the snail to food or to congre - they assimilate nutrients such as calci - gate with other snails. Snails have no um, magnesium and potassium, and ears, but they can detect vibrations. pass them to higher trophic levels when they are consumed by predators. Reproduction Snails are only one step above the Most of the land snails of Illinois are hermaphrodites, organisms that have The only predatory land snail in Illinois, both male and female reproductive the gray-footed lancetooth (above) extends organs. Although they are capable of its long neck into the shell of other snails. 10 / Outdoor Illinois June 2009 The rare carinate pillsnail possesses a flying saucer-shaped shell (left). The author’s (right) research focus has been the land snails of Illinois. The Fragile Existence of Land Snails in Illinois Euchemotrema hubrichti Frank Collins Baker, a famous mala - carinate pillsnail,, shell width 3/8 inch cologist (someone who studies mol - lusks), lived in Illinois during the 1930s base of the food chain, meaning there and wrote the “Fieldbook of Land Snails are plenty of predators relying on snails of Illinois,” published in 1939 (Illinois for their dietary needs. A great diversity Natural History Survey, Manual 2). of animal life feeds upon land snails, Although most of the species names are from insects to lizards and snakes, sala - outdated, it remains a useful guide. manders, birds and mammals. Some Notable from Baker’s range descrip - ) . k species of fireflies consume snails tions, as well as other field studies, r a l C e exclusively during their larval stage.