New Zealand Mud Snail
What are they?
New Zealand mud snails are tiny (less than 6 mm) aquatic snails that are adaptable to diverse climates and environmental conditions. They are found in freshwater and brackish environments.
Are they here yet?
Yes. New Zealand mud snails were first discovered in the lower Columbia River in 2002 and, on November 16, 2009, in Olympia’s Capitol Lake. Other known locations are include the lower Columbia River, the Long Beach peninsula, Kelsey Creek (King County), Thornton Creek (King County), and Lake Washington.
Why should I care?
New Zealand mud snails are considered a high invasive threat to freshwater and brackish water environments. They can dominate river and lakebed habitat by achieving densities of more than 100,000 per square meter. They out-compete native aquatic snails and insects that other species depend on for food. Disruption of the food chain can lead to reduced growth rates and lower populations of fish.
What should I do if I find one?
Do not purchase, plant, or trade this species. Call 1-877-9-INFEST or report online.
How can we stop them?
Clean, drain, and dry any watercraft after use—this prevents hitchhiking of any aquatic invasive species, including fish and shellfish diseases.
Thoroughly brush off any debris from waders, boots, and equipment that came in contact with stream or lake water, then wash the gear in hot water (140F), or freeze the gear overnight.
What are their characteristics?
New Zealand mud snails have five or six whorls and generally are light to dark brown, but can appear black in color, especially when wet.
Adults are 4-6 mm in length.
Generally self-reproducing by cloning — a single snail can rapidly reproduce and colonize a new area.
The opening of the shell has a movable cover called the operculum that allows the snail to seal itself inside, which protects it from short-term exposure to chemicals. It can survive out of water for weeks in damp, cool conditions, and it can pass-through the digestive tracts of fish and birds unharmed.
It can tolerate a wide range of habitats, including brackish water, and many different substrates such as rock, gravel, sand, and mud.
It is a nighttime grazer, feeding on plant and animal detritus, algae, sediments, and diatoms.
How do I distinguish them from native species?
Several species of native freshwater and estuarine snails can be confused with New Zealand mud snails because of their small size. A powerful magnifying loop or microscope may be needed to positively identify them.
Where can I get more information?