Scientific name: Potamopyrgus antipodarum

What Is It?

The New Zealand mud snail is a tiny (less than 6 millimeter) aquatic snail that is adaptable to diverse climates and environmental conditions. It is found in freshwater and brackish environments.

Is It Here yet?

Yes. New Zealand mud snails were first discovered in the lower Columbia River in 2002 and in Olympia’s Capitol Lake in 2009. Other known locations are in the lower Columbia River, Long Beach peninsula, and in King County’s Kelsey and Thornton Creeks 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 lake bed 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.

How Can We Stop It?

  • 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 Its 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 millimeters long.
  • Generally self-reproducing by cloning. A single snail can reproduce rapidly 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 It From Native Species?

Several species of native freshwater and estuarine snails may 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.

Additional Photographs