Inside N.C. Science: Freshwater snails vanishing from environment

Did you have an aquarium when you were growing up – or do you have one now? Did you have snails in it? In nature, our rivers, creeks and lakes are filled with freshwater snails … or were until recently.

Snails, also called gastropods, come in a variety of shapes: Some are round and smooth, others are tall and slender, some have ridges and a few have spines. Some even look like baseball caps. The outside of snail shells can be a solid color or striped. The largest native snail in the United States is the Florida applesnail. The smallest are some of the pebblesnails that live in springs in the desert Southwest; when fully adult are still less than 2 mm (0.08 inches) long.

You can find snails in many different aquatic environments, ranging from springs and small headwater streams to big rivers and alpine lakes.

Freshwater snails mostly lay eggs, either in clumps, lines or as single eggs. The most visible of these are the red egg masses deposited on cattail stems by the Florida applesnail. In North America there is a single family where the females do not lay eggs but give birth to active baby snails (called “live-crawl-away young”). These are the mysterysnails, such as the N.C. native, the banded mysterysnail.

All freshwater snails native to North America are algae feeders, scraping their food from the surface of rocks, logs or plant stems. Snails do not have teeth in the sense mammals do, but they do have a broad ribbon in the mouth that contains a battery of tooth-like structures arranged in a row that are used for scraping food. As these teeth wear out they are replaced by the row behind.

North America north of Mexico is home to 703 native freshwater snail species. The greatest diversity of freshwater snails can be found in the Alabama River system. North Carolina is home to 53 freshwater snail species.

Currently, a total of 67 freshwater snail species, including one whole genus, have become extinct from North America because of destruction of habitat, including damming, channelization or pollution. Seventy-four percent of existing North American freshwater snail species are at risk of extinction, far more than any other group of animals. To add to the stresses faced by freshwater snails, the aquarium trade recently has imported a carnivorous (snail-eating) snail into the U.S. Hopefully, this will never get introduced into North America’s rivers.

Arthur Bogan is research curator of aquatic invertebrates for the N.C. Museum of Natural Sciences.