Snail Relics

You’re walking through the woods and your eye catches a glimpse of something round and white. On closer inspection, it’s a shell, bleached chalky white with its former occupant long gone. Is this some remains of marine mollusks that dwelt here thousands of years ago or something more recent?

You haven’t found a fossil; you’ve found the shell of one of the numerous species of terrestrial snails roaming Montana. Some of the common names of species you might find in our part of Montana gives you an idea of how varied they are: ambersnail, glossy pillar, mellow column, forest disc, and quick gloss.

The live snails can be found under logs, leaf litter and duff. But keep your eyes out for the sun-bleached shells while you hike around Mountain Sky. Take pictures of the shells or bring them in to the ranch for display.

Here are descriptions of two species common to Paradise Valley.

Forest Disc (Discus whitneyi) Diagnostic Characteristics: A combination of shell shape (flattened heliciform or flattened conic), shell dimensions, number of whorls, shell color (olive-brown and chitinous), the presence of ribbing on the shell, lack of reflected lip, and absence of teeth in the aperture.   Habitat: Forested areas, from mesic (Engelmann spruce, Douglas-fir, secondary canopy including alder, mountain maple, dogwood, willow) to relatively dry (ponderosa pine and Rocky Mountain juniper, but usually in moister sites, such as imbedded pockets of aspen). Found under woody debris and rocks, in downed rotten wood, leaf litter and duff.

Subalpine Mountainsnail (Oreohelix subrudis) Diagnostic Characteristics: Medium to large size, calcareous whitish to gray (some may be brownish), moderately elevated spire (sometimes almost bee-hive shape), variable banding, relatively narrow umbilicus, absence of reflected lip, and surface sculpture help distinguish this from most other larger shells. Habitat: relatively moist sites, along stream courses and near seeps or springs, sometimes in talus slopes. Live animals present mostly in leaf litter, and under downed wood, rocks, and in duff or soil accumulations under wood and rocks.

Sources & Resources:

Montana Field Guide. http://fieldguide.mt.gov/displayFamily.aspx?order=Stylommatophora

Hendricks, P. 2012. A Guide to the Land Snails and Slugs of Montana. A report to the U.S. Forest Service - Region 1. Montana Natural Heritage Program, Helena, MT. vii + 187 pp. plus appendices.