Harmful Aquatic Hitchhikers: Mollusks: New Zealand Mud Snail

What do New Zealand Mudsnails look like?

New Zealand Mudsnails are small (3 to 6 mm or 1/8 inch) snails that have brown or black cone-shaped shells with five whorls.

Why are New Zealand Mudsnails considered to be a nuisance?

Densities & Competition with Native Species – This snail has the ability to reproduce quickly and mass in high densities. When snails become as dense as one-half million per meter square, this has been a cause for concern in western streams. Because the West is known for its great trout fishing, there is concern that the mudsnails will impact the food chain of native trout and alter the physical characteristics of the streams themselves. Research is needed to determine the impacts of large populations of mudsnails on the native fauna, such as aquatic insects and native snails, and on any changes in the physical environment.
Ability to Survive in Variable Conditions - The rapid spread of the mudsnail throughout the Yellowstone watershed may have been assisted by human transport. Mudsnails are able to withstand dessication, a variety of temperature regimes, and are small enough that many types of water users (anglers, swimmers, picnicers, pets) could inadvertently be the mechanism for interbasin transfer of this nuisance species.

How do New Zealand Mudsnails affect recreational users?

Anglers – Early research indicates that this group will probably be most impacted by the New Zealand Mudsnail. If this species does have a long-term impact, western trout fisheries could become devastated.

New Zealand Mud Snail

Where are New Zealand Mudsnails currently found?

In the late eighties, New Zealand mud snails were found in the Snake River in Idaho and the Madison River in Montana. As late as 1994, additional discoveries were made in the Madison River near the boundary of the Yellowstone National Park. Subsequent investigations by independent researchers have documented a rapid spread of this exotic species to the Firehole and lower Gibbon rivers. Snails have also been found in Lake Ontario, near the mouth of the Columbia River and in the Owens River in California.

What are New Zealand Mudsnails’ potential to spread elsewhere in U.S.?

There is great concern about this hitchhiker’s ability to spread because of its asexual reproduction and its ability to survive in harsh conditions. Because the mudsnails reproduce asexually, it only takes one individual to become introduced into new water to make an impact. Also, the mudsnails can readily attach themselves to boots and waders. So anglers must be vigilant in checking their gear and ensuring that it is free of mud and any noticeable snails.