California Aquatic Invasive Species (AIS)
University of California
California Aquatic Invasive Species (AIS)

Invasive Clams, Mussels, Snails, etc.

New Zealand Mudsnail

Scientific Name

Potamopyrgus antipodarum - Visit ITIS for full scientific classification. 



  • Very small, average size is around 1/8 of an inch, and can be as small as grain of sand.
  • Single grey, brown, or black shell with 5-6 spirals
  • Covered with a protected plate, called an operculum, when foot is retracted.
  • Easily confused with native snails such as Physa sp., Pyrgulopsis sp., Fossaria sp., Fluminicola sp., and others. 
  • Can be found over mud, sandy, or rocky substrates; and on vegetation.
  • Has a high tolerance to changes in water quality. 
Invasion Pathways and Distribution
  • Native to New Zealand.
  • Widely distributed in California.
  • Introduced into Idaho via shipment of fish eggs for hatchery operations.
  • Continued to spread via human activities including fishing.
  • Believed to have spread by attaching to recreational equipment including waders, boots and other fishing gear. 
  • Possibly dispersed by fish because they are capable of surviving passage through the digestive tracts.
  • Visit USGS for a current U.S. distribution map.
Life History
  • Nocturnal grazer.
  • Feeds on detritus, algae and sediments.
  • Live birth.
  • Females are born with developing embryos.
  • Individuals are capable of both sexual and asexual reproduction.
  • Outcompetes natives for resources.
  • New Zealand mudsnails themselves provide very low quality food for other animals, as most predators cannot digest the animal inside it's shell.
  • A single animal can start a new infestation due to asexual reproduction.
  • Can survive out of water by sealing it's shell, and can pass through a fishes' digestive tract.
References and Useful Links

For references by category and links to other useful AIS sites see our LEARN MORE page.

Top of page

Webmaster Email: