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Illinois Department of Natural Resources
August 2021
August 2, 2021
Photo by Ryan O’Connor, Wisconsin DNR.

Rare Algific Slopes Could Still Harbor Endangered Snail

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By Sheryl DeVore
A rocky slope with intermittent shrubs growing in-between the rocks, and there is a forest in the background.
Photo by Eric Epstein, Wisconsin DNR.

A rare geological feature in Illinois, the algific talus slope, harbors some of the state’s rarest plants and animals, including the federally endangered Iowa Pleistocene snail (Discus macclintocki). As the climate changes these and other flora and fauna could be in jeopardy.

An algific talus slope, which is steep and faces northward, is found in the driftless region of the United States, which encompasses parts of Illinois, Iowa, Wisconsin and Minnesota. In Illinois, the only place these slopes are found are within the Driftless Natural Division in Jo Daviess and Carroll counties. Glaciers missed that region, which allowed for certain features, such as algific slopes, to flourish.

“Usually no more than 100 feet by 100 feet in size, these small areas preserve a sample of what Illinois may have looked like during the last stages of the Ice Age 10,000 to 20,000 years ago,” wrote Susan Post in “The Driftless Area,” published by the Illinois Department of Natural Resources.

Kristen Lundh, who works with the U.S. Fish and Wildlife Service (USFWS) in Rock Island, said in an email that algific slopes found in other states, such as Iowa, are larger.

A dark green, brown snail foraging on a bed of green moss.
Photo courtesy of the USFWS.

Some of the rare plants growing in algific slopes can be found elsewhere in the world. But the Iowa Pleistocene snail can be found nowhere in the world except for the driftless zone in parts of Illinois and Iowa, said Duane Ambroz, Northwest District Heritage Biologist for the Illinois Department of Natural Resources. Most, if not all, are found in Iowa, but hope lingers that some still thrive in Illinois, likely on private property.

Just one-fourth-inch in diameter with brown to greenish shell, this snail was listed as federally endangered in 1978.

“It is dependent on cool, north facing vents, and its preferred foraging area is on sugar maple leaf duff,” Ambroz said. 

Fossilized shells show the snails were widespread in the Midwest more than 300,000 years ago, according to the USFWS. Illinois is thought to have once been the center of its distribution. 

A tiny tan, brown snail on a rock next to a penny.
Photo courtesy of the Iowa DNR.

The USFWS instituted a plan in 1984 to conserve the species. The plan included surveying sites where the snails live and the habitats they favored. A 2013 report showed snails live in about 38 sites in the driftless region, mostly in Iowa. More surveys were conducted later and the USFWS review published in 2020 showed that live snails “were present at fewer sties” compared with the 1980s. Introduction of non-native species such as garlic mustard and buckthorn, along with foot traffic in the fragile habitat, could be causing the decline.

The snails live in leaf litter where cool air and water, from underground ice, flow out of cracks in the slopes, keeping the ground temperatures cool in summer and warmer than surrounding areas in winter. The snails eat mostly birch and maple leaves on the forest floor. They also make tasty snacks for the short-tailed shrew.

Two tan, brown snail shells against a reddish orange background.
Photo courtesy of Iowa DNR.

The female snail may lay eggs several times spring through summer underneath logs or bark or into the soil. The snails can live to be five or more years old, and they hibernate beneath the ground in winter.

Kevin Roe, a professor at the University of Iowa, has explored the snail’s habitat in both Iowa and Illinois while doing genetic studies.

“We found some big genetic differences,” Roe said. That’s a good sign when it comes to preserving wildlife, because genetic diversity helps ensure their survival. 

Roe thinks conserving this species is important.

“The snail, along with other organisms that live on the algific slopes, have been experiencing climate change for thousands of years,” Roe said.

“You are looking at organisms that are on the forefront of climate change,” Roe continued. “In all honesty, I think we should be paying closer attention to these algific slopes. They are giving us a picture of the future. It is a great natural experiment of what’s going to happen,” if climate change continues.

A rocky cliff with a stream running below it.
Photo courtesy of the Iowa DNR.

The USFWS and other entities created the Driftless Area Project in the late 1980s to help protect the algific slope habitat. Since then, private homeowners have agreed to conserve that habitat on their properties, and that could be good news for the diminutive snail. Continued monitoring of the sites along with habitat restoration could help this species survive.

The USFWS believes this tiny, unassuming creature is a resilient animal that could adapt to global climate change. That’s one good reason to continue preserving and researching this little-known snail that hearkens to the Ice Age.


Sheryl DeVore writes environment and nature pieces for regional and national publications and has had several books published, including “Birds of Illinois” co-authored with her husband, Steven D. Bailey.

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