Dubuque County, Iowa
Note: This information is provided for reference purposes only. Although the information provided here was accurate and current when first created, it is now outdated.
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Iowa Pleistocene Snail
Table of Pesticide Active Ingredients
Limitations on Pesticide Use
|28||Do not apply within 100 yards of species habitat for aerial applications or within 20 yards of species habitat for ground applications.|
Iowa Pleistocene snail [Discus macclintocki]
The Iowa Pleistocene snail is an average sized snail with a mature width of 8 millimeters (0.5 in). The shell is tightly coiled, typically with six ribbed whorls, and is brown or off-white with a greenish cast. This snail feeds on the fallen leaves of white and yellow birch, hard maple, or occasionally dogwood and willow trees. It is most active from spring through summer but slows in early fall when the habitat dries. It remains near the soil surface until the first hard freeze, then burrows into the soil to hibernate.
The snail typically lives on rocky slopes over entrances to caves or cracks where ice is typically permanent underground. The ice helps to maintain the cool, moist conditions that the snail requires for survival. Rich, loose soil and scattered leaf litter also help to conserve moisture.
Like most North American snails, the Iowa Pleistocene snail is hermaphroditic, which means that each individual posesses both male and female reproductive organs, but is not self-fertilizing. All adults can lay eggs and fertilize other snails. The breeding season runs from March to August. Eggs are laid under logs and bark, in protected moist rock crevices, or just beneath the soil surface. Eggs take about 28 days to hatch.
This snail is an ancient creature. The species has existed for about 400,000 years, since the Pleistocene epoch or "Ice Age", when glaciers were advancing and retreating over North America. Currently, colonies of the snail can be found in Clayton and Dubuque counties in northeastern Iowa. There is also a colony in northwestern Illinois.
The major long-term cause of the decline of this species is cyclic climate change. The species was most abundant when glaciers were advancing and has dwindled during interglacial periods. However, scientists estimate that about 75 percent of the snail's habitat that existed 150 years ago has been destroyed by human activities, primarily deforestation that has been undertaken to obtain lumber, create pasture lands, or build roads. Natural factors such as forest fires, harsh seasons, and preying beetles and shrews also have contributed to the decline of this species. In addition, pesticides and herbicides have been sited as potential threats to the Iowa Pleistocene snail and its food sources. The U.S. Fish and Wildlife Service has developed a recovery plan and that includes habitat protection, research, reintroduction, and public education that will attempt to conserve this species.