Land Snails in the Desert: Nineteen Mollusk Species of Great Basin National Park

First published in The Midden, the Great Basin National Park newsletter, Vol. 19, No. 2, Winter 2019, by Mark Ports, retired professor at Great Basin College.

Snails in a desert?

Land snails and slugs in the Great Basin desert, with its salt-flat valleys, rivers that sink into the ground and long distances between high ranges, sound unlikely. Yet Great Basin National Park is home to 18 species of land snail and one slug — small and easy to miss.

The survey

From spring 2014 to summer 2016, a survey sampled more than 60 sites for land mollusks: canyons, wooded slopes and mountain brush, streamside woodland, subalpine lakes and bristlecone forests.

• Richest spot: wooded streamsides below limestone cliffs, such as the Grey Cliffs on Baker Creek, with 15 species.
• Why limestone: snails build their shells from its calcium carbonate.
• Why leaf litter: damp litter under shrubs and aspen feeds these plant-eaters and keeps moist the mucus they glide on with their single foot.
• Streamside habitat with broadleaf plants, damp litter and rockslides can hold 8 to 12 species. Rockslides are deep, damp refuges from summer heat and winter cold.
• Boggy stream banks and wet springs can hold up to 11 snail species, plus the park's only slug, Deroceras laeve, and the water-loving ambersnails (family Succineidae).

High and low

• Highest: rocky bristlecone woodland at 3,200 meters, with only 1 to 3 species.
• Lowest: sagebrush steppe at 1,800 m, with only 2.
• The dry, bare ground under much of the pinyon pine and Utah juniper woodland seems to support none.

Big and small

• Most are tiny, 2–6 mm across — such as the Montane Snaggletooth (Gastrocopta pilsbryana), only 2 mm long, and the Crestless Column (Pupilla hebes).
• The largest are mountainsnails (family Oreohelicidae), 10–20 mm across, living in local colonies in rockslides sheltered by shrubs, aspen and conifers:
• • the Schell Creek Mountainsnail (Oreohelix nevadensis), found only in Nevada;
  • the Great Basin Mountainsnail (Oreohelix strigosa depressa), in the mountains of eastern Nevada and many ranges in Utah and Colorado.

Ice Age survivors

The park's land mollusks are close kin to those of northeastern Nevada, such as the Ruby Mountains, and share many species with Utah's Wasatch Mountains. They are probably remnants of a community that spread across the Great Basin and the Rockies in the wetter Pleistocene, and that retreated uphill to damp, wooded mountains as the climate dried.

Today they cling to small, specialized habitats, and climate change and human disturbance make their future uncertain.

Read more: M. A. Ports, "Terrestrial mollusks of Great Basin National Park, the Snake Range, Nevada, USA," Western North American Naturalist 79(2): 247–259, 2019. Next in this issue: Bonneville cutthroat trout reintroduced to Snake Creek.

Sources

Based on "Nineteen Species of Terrestrial Mollusks Found in Park," by Mark Ports, The Midden — Great Basin National Park, Vol. 19, No. 2, Winter 2019; published by the National Park Service and in the public domain; rewritten in hubnx's own words. The author's photographs are not reproduced. The source spells the slug's genus Derocerus and the ambersnail family Succiniedae, and dates the dry Holocene to the last 50,000 years; this page uses the standard spellings and leaves that figure out.