Animal Type: Molluscs
Family: Gastropoda
Classification: Prohibited

U.S.G.S. FISC - Center for Aquatic Resource Studies

Mudsnail ID card - USFWS

The New Zealand mud snail was first found in the Snake River in Idaho in 1987. By 1997 there was a population in the Madison River in Yellowstone Park. In some areas they were in densities of up to 750,000 per square yard. Since then they have been found in the Colorado, Upper Missouri, Owens, Columbia and other Rivers. In Washington there are established populations in the Columbia River at Young’s Bay and Kalama, in the Snake River on the eastern border of the state, and in a number of private waterways on the Long Beach Peninsula.

New Zealand mudsnails are small (about 1/8 – 1/4 of an inch long when full grown) that have brown or blackish cone-shaped shells with five whorls. They tolerate a broad range of temperature, salinity, and water quality, and have no natural parasites or predators in the United States. They are able to close their shells, and live out of the water for quite some time. Unfortunately, it only takes one to begin a new population. Females “clone” themselves, producing up to 38 new female snails each year. Each offspring in turn reproduces itself, so that in two years there may be over 3.5 million snails carpeting the bottom of a river or lake. Preliminary studies indicate that in areas where they have become densely populated they are impacting the invertebrate populations via displacement and competitive interactions. Large populations may consume up to half of the available food in a stream, starving out insects essential to trout and salmon. The snails are very small - between an eighth and a quarter inch in size – and may not be noticed attached to tackle, waders, boats, etc.

Boaters and anglers can help prevent the spread of Aquatic Invasive Species by observing the following precautions.

• Before leaving a waterbody, remove all plants, algae, or mud from shoes, waders, life vests, boat hulls, trailers, and other gear.
• Clean all equipment with a decontamination treatment ensuring that porous materials such as felt sole waders are thoroughly soaked to ensure full penetration. Soak equipment for 5 minutes in a 5% solution of household detergent or dishwashing liquid, salt, diaper cleaner, antiseptic hand, or a 2% bleach solution. Felt soled waders should be soaked for at least 30 minutes. Choose a decontamination solution that will not adversely affect your equipment, and use the hottest water available. Dispose of the solution away from any waterbodies.
• If using a decontamination solution is not practical, once the item is completely dry to the touch, wait an additional 48 hours to ensure the item is thoroughly dry before contact or use in another waterbody. Felt soled waters require additional drying time.

*Laboratory tests show that the snails, as well as other invasive species and pathogens such as Didymosphenia gemnata (Didymo) or Myxobolus cerebralis (whirling disease) live longer in felt sole waders because they remain damp for so long. We recommend always using a decontamination treatment.

For more information go to:

http://www.protectyourwaters.net/hitchhikers/mollusks_new_zealand_mudsnail.php
http://www.nps.gov/yell/planvisit/todo/fishing/mudsnail.htm
http://www.esg.montana.edu/aim/mollusca/nzms/