From a visitor from England who visited Calgary on the way to Juneau, I learned about the Banff Springs snails, which live in thermal springs with temperatures up to just over a hundred degrees Fahrenheit, often having low oxygen and high hydrogen sulfide. That sparked my interest. I wanted to learn more about them and about other snails that might live in hot springs. So I was launched on a little voyage of discovery.
The Banff Springs snails (Physella johnsoni) live in only a few hot springs in Banff National Park in Alberta. They are small, averaging about the size of a corn kernel or a lemon seed and reaching a maximum of about one centimeter. They breathe air and feed chiefly on algal mats growing on rocks and vegetation. Being hermaphroditic (having both male and female sex organs), they often self-fertilize but they can also mate with each other. Preferred water temperatures range from about 85 to 97 degrees Fahrenheit. The snails tend to aggregate near where the thermal waters bubble up, so fewer are found downstream.
Another snail of this genus lives in the Liard Hot Springs in British Columbia. Both are related to a third species (P. gyrina) that is widespread in North America, reportedly including the southernmost tip of Southeast Alaska. The Banff species is estimated to have diverged from P. gyrina about 10,000 years ago—or perhaps only about 4,000 years ago.
The taxonomic family (Physidae) to which these snails belong contains many species, most of which do not live in hot springs. Members of this family (including one very invasive species) occur throughout the Americas and the Old World. All of them are hermaphroditic and air-breathing. They are characterized by having shells with a left-handed spiral, unlike most other snails. (When you hold up a snail with the shell point up and the opening down and facing you, a left-handed spiral opens on the left…in contrast to the right-handed spiral that opens to the right). Embryos in the eggs hatch directly into small snails. Those that live in hot springs have a fast life cycle, maturing at an age of six months and able to reproduce all year long because they do not hibernate.
Very different hot-spring snails live in certain places in North America (Oregon, Idaho, New Mexico). They are not closely related to Physella, but belong to a different taxonomic family, the Hydrobiidae. Only some species of this large genus (Pyrgulopsis) live in hot springs, typically preferring water temperatures of about seventy-five to ninety-five degrees Fahrenheit. These minute snails have right-hand spirals and separate sexes, with the females typically larger than the males. And they do not breathe air but use gills to extract oxygen from water. I have not yet found information about age of maturation and hibernation, but it seems likely that these would also have a fast life cycle.
Thinking about all those freshwater snails that live in hot springs reminded me of the animals that inhabit deep-sea thermal vents, whose water temperatures reach very high levels (over 750 degrees Fahrenheit. Sure enough, there is a snail in the Indian Ocean that lives there too, but just at the margins of the vent area, where it lives at 36 to 50 degrees Fahrenheit. This one is named the scaly-foot gastropod (genus Chrysomallon), so named for the iron-clad scales on the external surface of its foot (there’s another story there, I’m sure…).
Alaska has lots of hot springs, especially in the Aleutians and the Alaska Peninsula, but also in Southeast and elsewhere. But I have found no reports of snails living in them, just a mention of snails along the edges of the springs.
• Mary F. Willson is a retired professor of ecology. “On The Trails” appears every Wednesday in the Juneau Empire.
