Of Mountains and Snails
by Krys Standley
Broadcast 9.28 & 10.1.2021
On a mid-afternoon outing some years back, my young children and I made our meandering way across a flat mountain bench near our home. Hiking with children is, at its best, an exercise in being unhurried, a practice of noticing the little things and delighting in small moments. As we entered a conifer thicket, we happened upon an animal I was not expecting on dry land – a snail – creeping along the curved trunk of a young fir tree.
I was used to seeing snails in streams and ponds, crawling underwater in their small, tapering, pointed shells, and I thought all snails in this area were aquatic. This snail was different. Its shell was larger and grew in a flattened, disk-shaped form. The subtle brown stripes spiraling outward from its shell’s midpoint camouflaged the snail perfectly against the tree. As the three of us looked on, it made its way, leisurely, along the rough bark of the tree’s bent trunk, leaving behind a liquid silver trail. This was my first encounter with a live terrestrial snail in Montana, though in retrospect I realized I had seen their remains before: translucent, white, empty shells nestled among the duff on dry mountain slopes.
As it turns out, Montana is home to many types of terrestrial snails: 80 distinct species, hailing from 17 different families, make their homes here. Like aquatic snails, they belong to the class of mollusks called gastropods. In Latin, the word gastropod derives from gaster, or “belly” and podus, or “foot.” Literally “belly-footed,” snails contract and relax their ventral muscles in a wave-like action to move about their home territory.
One well-represented family of terrestrial snails in Montana is the mountain snail, which is well adapted for our often-arid climate. Mountain snails tend to be active in late spring and again in early fall when temperatures are mild and the season is rainy. To survive our dry summers, they burrow underground and enter a state of dormancy. Mountain snails also have a unique method to protect their young from dry spells. In contrast to most terrestrial snails, which lay their gelatinous eggs in exposed nest holes in the soil – a hazardous practice because the eggs can dry out before they have time to hatch – mountain snails hatch their young internally, later giving birth to live, well-developed juveniles that have already grown two to three shell whorls, half the number they will have at maturity.
If you live in Western Montana, you don’t have to go far to be in mountain snail territory; several species are widespread and common. The Missoula Mountainsnail, for instance, is found on Mount Jumbo and Mount Sentinel, just outside of town, and the Rocky Mountainsnail is found on both sides of the Continental Divide – spanning 22 Montana counties. Even so, finding them is not easy. They spend much of their lives underneath duff and leaf litter on the forest floor. It is here that mountain snails find their favorite food: decaying vegetation, which they eat by scraping off small bits with a blade-like mouth structure called a radula.
Aside from moisture and food, mountain snails have another basic need: they require calcium to build their shells. Fortunately for mountain snails, calcium is readily available from limestone and its associated mineral-rich soils that are abundant throughout Montana. Mountain snails consume this calcium either directly or from plants that concentrate calcium in their leaves.
Across the state, limestone can be seen in deposits like the Chinese Wall in the Bob Marshall Wilderness and the cliffs of Gates of the Mountains, north of Helena. These high and dry limestone deposits have an aquatic connection. They are a conglomeration of the skeletal remains of invertebrate sea creatures from the Paleozoic Era – when the ocean rose to submerge much of what is now Montana under shallow seas. This sediment accumulated and compressed for hundreds of millions of years to become the limestone we see today. So, in a way, mountain snail populations depend on the geological memories of their ancestors.
In contrast to the long game of the geologic time frame, the pace of daily life is brisk. My children are now young adults and, without the need to slow down for them any longer, I enjoy the ability to cover ground more quickly. Still, I am ever fascinated by the up-close noticing that can happen when I take more time. Just this past spring, when checking out a mushroom growing along a local hiking trail, I encountered another live terrestrial snail.
Every week since 1991, Field Notes has inquired about Montana’s natural history. Field Notes are written by naturalists, students, and listeners about the puzzle-tree bark, eagle talons, woolly aphids, and giant puffballs of Western, Central and Southwestern Montana and aired weekly on Montana Public Radio.
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