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Driftless Area
National Wildlife Refuge

Box 460
McGregor, Iowa 52157
(563) 873-3423

 

 


 

 

Iowa Pleistocene Snail Iowa Pleistocene Snail

Photo by Bob Clearwater

These small land snails are only about 1/4-inch in diameter.

A tiny snail, a relict from the ice age finds home on a cool rocky slope, near the coldwater streams, cliffs, valleys, and sinkholes that make up the Driftless Area National Wildlife Refuge in Iowa. The endangered Iowa Pleistocene snail (Discus macclintocki) has known the meaning of refuge in more ways than one. Known from fossil records to have existed 400,000 years ago, it is one of many glacial relict species that found refuge in the region of northeast Iowa, northwest Illinois, southeast Minnesota, and southwest Wisconsin called the driftless area. The rugged driftless area was so called because of early geologist’s inability to find glacial drift. Much of the area was indeed covered by glaciers about 500,000 years ago. The Iowa Pleistocene snail found its current home with desirable temperature, moisture, and food resources about 10,000 years ago as ice age conditions moderated. Certain slopes, usually north facing, have loose rock that allows ice-cooled air to exit from underground cracks and fissures. Upland sinkholes contribute to the air flow regime and are an important component of a unique system called an algific talus slope, meaning cold producing rocky slope. Even when outside air temperature is 90 degrees, ground temperatures on these slopes can be close to freezing. This air flow provides a climate similar to what was prevalent in glacial eras. Freezing winter temperatures are moderated on the slopes giving a year round range of about -10 to 10o C (14 to 50o F).

The Iowa Pleistocene snail now occurs nowhere else in the world but 37 algific talus slopes in Iowa and Illinois. The Iowa Pleistocene snail was thought to be extinct until discovered in 1955 by a scientist working in northeast Iowa. It was listed as endangered in 1977. It is no bigger than a shirt button with adults ranging in size from 5 to 7 millimeters in diameter. They live in the leaf litter preferring a diet of birch and maple leaves. The snail shares its habitat with a host of rare and disjunct plants and animals associated with cool habitats. Balsam fir (Abies balsamea), Canada yew (Taxus canadensis) and yellow birch (Betula alleghaniensis)are common to algific talus slopes. The threatened Northern monkshood plant (Aconitum noveboracense) also grows on these sites. More abundant on approximately 114 sites in Iowa, Wisconsin, Ohio and New York monkshood also grows on similar cool moist habitats like sandstone cliffs. The majority of sites are in Iowa. The perennial monkshood is a member of the buttercup family and derives its name from the hood shape of its zygomorphic flowers adapted for bumblebee pollination.

The 775 acre Driftless Area National Wildlife Refuge was established in 1989 to permanently protect populations of the Iowa Pleistocene snail and threatened Northern monkshood. These species’ habitat cannot be restored once lost and the primary objective of their respective recovery plans is providing protection for remaining colonies. Concern over threats to the habitat stemmed from logging, grazing, filling of sinkholes, agricultural runoff, roads and quarries. The invasion of garlic mustard (Alliaria petiolata) onto algific talus slopes has emerged as a threat in recent years. And no one knows the potential effects of modern global warming.

The Refuge consists of scattered tracts of land in northeast Iowa ranging from six to 208 acres. Algific talus slopes range in size from a few square meters to perhaps ½ mile in length. More than just the algific talus slope is targeted for acquisition. Sinkholes that feed the system can occur some distance away from the slope and need protection to ensure long term integrity of the site. Buffer areas around the slope are included when possible. The Refuge contributes to lands already protected by The Nature Conservancy, the Iowa Department of Natural Resources, County Conservation Boards in Iowa, and publicly owned sites in Ohio and New York. Further acquisition is planned to reach recovery goals. A 1993 expansion proposal is being considered under recently initiated comprehensive conservation planning for the Refuge to include counties in Minnesota where the threatened Leedy’s roseroot (Sedum integrifolium spp. leedyi) occurs. Listed in 1992, it occurs on only four sites in southeast Minnesota and three in New York. Refuge expansion would provide more protection for Northern monkshood and other glacial relict snails as well. In a cooperative effort with the Refuge, Iowa and Wisconsin recently received Section 6 recovery funding to purchase two Northern monkshood sites.

At least eight other snail species, considered glacial relicts, are also protected on these sites. Some of these species like the midwest pleistocene vertigo (Vertigo hubrichti hubrichti), are even smaller and perhaps more rare than the Iowa Pleistocene snail. Protection of algific talus slopes may help prevent the need for threatened or endangered status for these snails and plants like the golden saxifrage (Chrysosplenium iowense).

There are over 300 algific talus slopes in Iowa, with varying species components. Not all slopes have all of these species. Some may not have federally listed species and are more conducive to protection by local agencies and groups. Private landowners are the stewards of many algific slopes. Landowners with federally listed species on their property were contacted by the Refuge and The Nature Conservancy and funding under the Service’s Endangered Species Landowner Incentives Program allowed fencing to be completed to exclude cattle from five algific talus slopes.

Of course, the goal is recovery. To gauge progress over the years, monitoring of Northern monkshood is conducted and we are experimenting with monitoring methods for the Iowa Pleistocene snail. A mark recapture study was initiated in 2000 with the assistance of Iowa State University. The Nature Conservancy of Iowa placed an intern at the Refuge office this year to conduct monitoring for both species and TNC preserves. The Iowa DNR has assisted with monitoring and identification of acquisition sites. With all of these efforts and barring extensive global warming, these species can someday be recovered as representatives of ice age history.

Iowa Pleistocene Snail

Why is the Iowa Pleistocene Snail Endangered?

Habitat Loss or Degradation - The major long-term cause of snail population decline is climate change. The most immediate habitat threats are from logging, quarrying, road building, sinkhole filling and contamination, human foot traffic, livestock grazing and trampling, and misapplication of pesticides.

What is Being Done to Prevent Extinction of the Iowa Pleistocene Snail?

What Can I Do to Help Prevent the Extinction of Species?


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