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Carychium exiguum

What do they look like?

Obese thorn snails are small snails. They have white, long shells that are 1.2 to 2.5 mm tall, with about 4.5 spirals. The body of the snail is smooth. There is a single pair of tentacles that can be drawn in, and eyes are located at the base of the tentacles. (Bashynski, 2008; Burch and Jung, 1988; Harry, 1997; Perez and Cordeiro, 2008)

  • Sexual Dimorphism
  • sexes alike
  • Range length
    1.2 to 2.5 mm
    0.05 to 0.10 in

Where do they live?

Carychium exiguum, the obese thorn snail, is native to North America. It ranges north in Canada from Newfoundland to central Manitoba (areas including Alberta, New Brunswick, Nova Scotia, Ontario, Quebec, and Newfoundland), west to New Mexico and the Sierra Madre mountains in Mexico, south to Costa Rica, and east to the Atlantic coast. It is common through the middle and eastern United States, and in many states is the most abundant species of land snail. This species has also been recorded in central Oregon. In Michigan, obese thorn snails are found throughout the state. ("Carychium exiguum", 2003; Burch and Jung, 1988; Hubricht, 1985; Nekola, 2005; Perez and Cordeiro, 2008)

What kind of habitat do they need?

Obese thorn snails are found in very damp areas, such as floodplains, swamps, and moist woodlands. These snails generally live in areas with moss, ferns, and plant debris, in shaded areas such as under leaf litter or rotting logs. In Michigan, three habitats have been described for this species: small depressions in cypress (Thuja sp.) forests, grasslands, and hardwood forests. (Bashynski, 2008; Burch and Jung, 1988; Harry, 1997; Miller, 1970; Perez and Cordeiro, 2008)

How do they grow?

Land snails lay their eggs in moist areas. These snails have a shell gland, which produces a leathery covering for the eggs. The timing of the eggs hatching depends on moisture and temperature. Typically, these snails grow throughout the summer after hatching, reaching near-adult size by mid-fall, though this may vary between populations. Snails are considered adults when the ridge around the opening of the shell becomes thick. (Burch and Pearce, 1990; Geraerts and Joosse, 1984; Harry, 1997)

How do they reproduce?

Obese thorn snails are hermaphrodites, meaning that each snail has both male and female genitalia. These snails reproduce by cross-fertilization, with two snails mating and fertilizing each other. A snail may find a mate by following the mucus trails left behind. They usually have a courtship ritual before mating. During mating, each snail inserts sperm into the other snail. Both snails will produce eggs. (Burch and Pearce, 1990; Geraerts and Joosse, 1984; Harry, 1997)

Obese thorn snails likely hatch in late spring or early summer and reach adulthood in the fall, particularly in temperate areas such as Michigan. Thick edges at the opening of the shell show that the snails are able to mate. These snails produce about three eggs at a time. (Geraerts and Joosse, 1984; Harry, 1997; Geraerts and Joosse, 1984; Harry, 1997; Geraerts and Joosse, 1984; Harry, 1997; Geraerts and Joosse, 1984; Harry, 1997; Geraerts and Joosse, 1984; Harry, 1997; Geraerts and Joosse, 1984; Harry, 1997)

  • How often does reproduction occur?
    Obese thorn snails reproduce once yearly.
  • Breeding season
    Obese thorn snails likely reproduce in the spring and early summer.
  • Average number of offspring

After obese thorn snails lay their eggs, they leave them and do not provide any parental care. (Burch and Jung, 1988)

  • Parental Investment
  • no parental involvement
  • pre-fertilization
    • provisioning

How long do they live?

Obese thorn snails likely live about 1 year. (Harry, 1997; Harry, 1997; Harry, 1997)

  • Average lifespan
    Status: wild
    1 years

How do they behave?

Obese thorn snails are active during the night, and are also more active when there is more humidity and cooler temperatures. During dry periods and during the winter, a membrane will form over the opening of the shell and seal the shell off. This prevents the snail from losing water and allows it to survive until conditions improve. Obese thorn snails are often found gathered in small groups, typically under leaves. When crawling along, the head of the snail emerges from the shell, and the shell moves from side to side as the snail moves forward. The tip of the tail also jerks. These snails move slower when wet. (Burch and Pearce, 1990; Harry, 1997; Pearce, 1989; Burch and Pearce, 1990; Harry, 1997; Pearce, 1989)

  • Range territory size
    10 (high) m^2

Home Range

Smaller species of snails, such as obese thorn snails, live in about 10 square meters of space. (Burch and Pearce, 1990; Nekola, 2012)

How do they communicate with each other?

Obese thorn snails have sensory tissue at the tips of their tentacles. Land snails leave mucus trails which are used as a form of communication between other snails. The mucus allows the snails to detect individuals of their own and other species. They also have eyes located at the bases of their tentacles and can detect light, though they tend to avoid it. (Burch and Pearce, 1990; Harry, 1997)

What do they eat?

Obese thorn snails use an organ called a radula to feed. The radula is covered in teeth, and is used to scrape or grind food. These snails feed on decaying plant material and fungi.

  • Plant Foods
  • leaves

What eats them and how do they avoid being eaten?

Obese thorn snails are preyed on by beetle larvae or other insects, birds, rodents, and small mammals, particularly voles and shrews. (Burch and Pearce, 1990)

What roles do they have in the ecosystem?

Land snails usually move seeds and fungal spores to other areas, so the seeds can grow in new areas. They also break down decaying matter on the forest floor, by eating it and digesting it. Obese thorn snails are also prey to a variety of animals, including insects, birds, and small mammals. (Burch and Pearce, 1990; Harry, 1997)

Do they cause problems?

Obese thorn snails do not cause any problems for humans.

How do they interact with us?

Obese thorn snails do not have any known positive effects on humans.

Are they endangered?

Obese thorn snails are not an endangered species. (IUCN, 2013)

Some more information...


Renee Mulcrone (author), Special Projects, Angela Miner (editor), Animal Diversity Web Staff.


2003. "Carychium exiguum" (On-line). Encyclopedia of Life. Accessed May 16, 2013 at

Bashynski, S. 2008. "Carychium exiguum (Say, 1822)- Obese Thorn" (On-line). BioWeb. Accessed December 15, 2013 at

Burch, J., Y. Jung. 1988. Land snails of the University of Michigan biological station area. Walkerana, 3/9: 1-177.

Burch, J., T. Pearce. 1990. Terrestrial gastropoda. Pp. 201-310 in D Dindal, ed. Soil Biology Guide. New York: John Wiley and Sons.

Geraerts, W., J. Joosse. 1984. Freshwater snails (Basommatophora). Pp. 141-207 in A Tompa, N Verdonk, J van den Biggelaar, eds. The Mollusca, Vol. 7, reproduction. London: Academic Press, Inc.

Harry, H. 1997. Carychium exiguum (Say) of lower Michigan; morphology, ecology, variation and life history (Gastropoda, Pulmonata). Walkerana, 9/21: 1-104. Accessed August 19, 2013 at

Hubricht, L. 1985. The distributions of the native land mollusks of the Eastern United States. Fieldiana, Zoology New Series, 24: 1-191. Accessed August 19, 2013 at

IUCN, 2013. "The IUCN Red List of Threatened Species. Version 2013.2" (On-line). Accessed August 19, 2013 at

Miller, B. 1970. The Sandahl molluscan fauna (Illinoian) from McPherson County, Kansas. Ohio Journal of Science, 70/1: 39-50. Accessed December 15, 2013 at

Nekola, J. 2005. Geographic variation in richness and shell size of eastern North American land snail species. Records of the Western Australian Museum, Supplement 68: 39-51. Accessed December 15, 2013 at

Nekola, J. 2012. The impact of a utility corridor on terrestrial gastropod biodiversity. Biodiversity and Conservation, 21: 781-785. Accessed August 19, 2013 at

Pearce, T. 1989. Loping locomotion in terrestrial gastropods. Walkerana, 3/10: 229-237. Accessed August 19, 2013 at

Perez, K., J. Cordeiro. 2008. A guide for terrestrial gastropod identification. Terrestrial Gastropod Identification Workshop, 1: 1-72. Accessed December 15, 2013 at

University of Michigan Museum of ZoologyNational Science Foundation

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Mulcrone, R. 2014. "Carychium exiguum" (On-line), Animal Diversity Web. Accessed April 19, 2024 at

BioKIDS is sponsored in part by the Interagency Education Research Initiative. It is a partnership of the University of Michigan School of Education, University of Michigan Museum of Zoology, and the Detroit Public Schools. This material is based upon work supported by the National Science Foundation under Grant DRL-0628151.
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