Iowa pleistocene snail (Discus macclintocki)
|Size||Adult shell width: 6 - 8 mm (2)|
- The Iowa Pleistocene snail is endemic to North America, and is considered to be an Ice Age relic.
- The Iowa Pleistocene snail is thought to have been widespread throughout the Midwest during the Pleistocene epoch, hence its name.
- An adult Iowa Pleistocene snail has a dome-shaped shell with six whorls.
- Iowa Pleistocene snails are hermaphrodites, but do not self-fertilise. They are thought to be able to both lay eggs, and fertilise others.
The Iowa pleistocene snail is classified as Least Concern (LC) on the IUCN Red List (1).
The Iowa Pleistocene snail (Discus macclintocki) is an average-sized snail within the genus Discus (2). The dome-shaped shell is tightly coiled, adults typically have six whorls with an overall shell width of six to eight millimetres (2) (3). The shell is brown to greenish-white in colour, with an open hole on the underside of the shell in the centre of the whorls, called the umbilicus, and many, close-set ribs (2) (3).
Based on fossil evidence, it is thought that the Iowa Pleistocene snail was widely distributed throughout the Midwest during the Pleistocene epoch (2) (4). However, by 1984, the Iowa Pleistocene snail was restricted to 18 small areas within north-western Iowa and north-western Illinois (2) (4).
The Iowa Pleistocene snail can be found among leaf litter, on algific talus slopes (2) (5) (6). These are ‘cold producing’ slopes that maintain cool and moist soil throughout summer as a result of a complex interaction between the local geology, topography, ecology and hydrology (2) (5) (6). Ground temperature rarely exceeds 10°C or falls below -10°C (2).
The Iowa Pleistocene snail retreats into the soil around October to hibernate, although this may occur earlier if it is particularly cold. The snails hibernate until March or April when the ice thaws (2).
Breeding season is confined to between March/April to August. The Iowa Pleistocene snail is hermaphroditic, as are most North American land snails, but they are not self-fertilising. They are reported to be able to both lay eggs and fertilise others. Iowa Pleistocene snails lay their eggs under logs, in rock crevices or in the soil. The gestation period is not known, but individuals have been observed to have several broods a year. The average clutch size is three, and hatching occurs about 28 days after the eggs are laid, commonly with a 90 percent hatch rate (2).
In captivity, Iowa Pleistocene snails required between two and two and a half years to reach sexual maturity. Juvenile snails are much more active than adult Iowa Pleistocene snails. They are typically the last to hibernate, and the first to emerge in the spring, but they are more susceptible to drying out than adults, and are less often seen outside the confines of a colony as a result (2).
An important, long-term threat to the Iowa Pleistocene snail is climate change, and a subsequent loss of habitat (6). The algific talus slopes are also threatened by human disturbance and overgrazing (5) (6). As well as directly crushing individuals, these threats can cause compaction of the vents that maintain the cool moist soil that the snails are dependent on (6).
Drying out is a significant threat to Iowa Pleistocene snails, particularly for juveniles. Predation by the short-tailed (Blarina brevicauda) shrew is also an important threat to the Iowa Pleistocene snail. The short-tailed shrew noticeably prefers large adult snails and tends to ignore juveniles (2).
As a result of a recovery plan issued by the US Fish and Wildlife service in 1984 the number of known colonies increased from 19 to 37 in 2009. 24 of these colonies were known to be present in some kind of protected area. According to the US Fish and Wildlife service in 2009, the overall population status was labelled as ‘stable’, though they still class the Iowa Pleistocene snail as endangered due to the threats to their habitat that still remain (7).
Find out more about the Iowa Pleistocene Snail:
The Nature Conservancy:
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- Algific talus slopes: A rare and unique habitat type created due to underground processes that produce cold air. This air helps to keep the soil aboveground cool and moist, even when temperatures increase during the summer.
- Genus: a category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.
- Gestation: the state of being pregnant; the period from conception to birth.
- Hermaphroditic: possessing both male and female sex organs.
- Hibernate: hibernation is a winter survival strategy in which an animal’s metabolic rate slows down and a state of deep sleep is attained. While hibernating, animals survive on stored reserves of fat that they have accumulated in summer.
- Pleistocene: a geological time period from approximately 2 million years ago until 10,000 years ago.
- Umbilicus: in gastropod molluscs, such as snails, a depression or hole on the underside of the shell, at the centre of the whorls (the spirals or coils of the shell). It is present in many but not all snail species.
- Whorls: the spirals or coils in the shell of a snail.
Red List (November, 2013)
- Frest, T.J. (1984) National Recovery Plan for Iowa Pleistocene Snail (Discus macclintocki). Fish and Wildlife Reference Service, Maryland
- Pilsbry, H.A. (1939) Land Mollusca of North America: (north of Mexico). Wickersham Printing Company, Pennsylvania
- Cavendish, M. (2001) Endangered Wildlife and Plants of the World.Marshall Cavendish Corporation, New York
- Ney, J., and Nichols, T. (2009) America’s Natural Places: The Midwest. ABC-CLIO, California
Iowa Department of Natural Resources. Iowa Pleistocene Snail: Discus macclintocki Landowner Incentive Program, US Fish and Wildlife Service
Iowa Pleistocene Snail (Discus macclintocki) 5-Year Review: Summary and Evaluation.US Fish and Wildlife Service