New Zealand mudsnails, an invasive snail species, have been verified in two new streams in Dane County: Brewery Creek and Badfish Creek. Their identification marks the first time that these tiny foreign snails have been found in the Rock River watershed.
Because New Zealand mudsnails are sticky and small — about 4 to 6 millimeters long, the size of a grain of rice — they can easily get stuck in the crevices of boots, waders, fishing gear and other equipment.
To reduce the spread of invasive mudsnails to other streams and bodies of water, the Wisconsin DNR is asking anglers to inspect their boots and fishing equipment for snails, brush off mud in which snails can hide, rinse equipment with tap water away from streams and waterbodies, and freeze gear for at least eight hours.
New Zealand mudsnails can tolerate a wide range of environments and have been found in nearly every freshwater habitat in their native country. They were first discovered in the United States in Idaho in 1987, most likely carried by ballast water used to balance cargo ships or imports of contaminated game fish.
The snails were first identified in Wisconsin in 2013 in samples from Black Earth Creek in western Dane County. Other populations have since been found in the Duluth-Superior Harbor on Lake Superior and Waukegan Harbor on Lake Michigan. Although the snails do not require a mate to reproduce, the population doesn’t seem to be expanding, according to the Wisconsin Department of Natural Resources. It’s unknown how the mudsnail will affect local ecosystems, but it’s possible they could outcompete native stream insects that are food for fish.