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Alligatorweed (Alternanthera philoxeroides)
Photo credit: Robyn Draheim

New Zealand Mudsnail

(Potamopyrgus antipodarum)

Report this Species!

If you believe you have found this species anywhere in Pennsylvania, please report your findings to iMapInvasives by submitting an observation record.

Species at a Glance

The New Zealand mudsnail is a tiny aquatic snail that multiplies quickly and disrupts the food chain. Its small size makes it easy for anglers and boaters to unknowingly transport it from one body of water to another, and since it reproduces asexually, it takes only one snail to start a new population.


The shell is long, narrow, and coiled to the right in up to eight whorls that come to a point at the top of the shell. Each whorl is separated by deep grooves. Some morphs, such as those in the Great Lakes, can have either smooth shells or shells with a keel in the middle of each whorl. Average adult size in an invasive population is only 3-6 mm (0.1-0.2 in). Color varies from gray to light and dark shades of brown. An ear-shaped operculum covers the opening of the shell.

Similar Species

While it can resemble many different species of native snail, the New Zealand mudsnail is usually more narrow, longer, and has more whorls than most native snails in the same genus.


The New Zealand mudsnail is known to inhabit freshwater ponds, streams, rivers, lagoons, lakes, ditches, and reservoirs. It has a wide range of tolerances for substrate, temperature, and salinity, and can survive in brackish water.


The operculum, which is a small cover that can be used to close the opening of the shell, allows the New Zealand mudsnail to survive out of water and hitchhike on recreational boating or fishing equipment, the feet of wildlife, feathers, and fur. It can also pass through the digestive system of predators alive and undigested.


While native to New Zealand, this mudsnail was accidentally introduced into the United States in the 1980s, possibly with the transfer of fish eggs and live game fish, or in the ballast water of transoceanic ships. The only occurrences in the Mid-Atlantic region are in New York and Pennsylvania.


Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.

Environmental Impacts

The New Zealand mudsnail reproduces rapidly, displacing native species of mollusks and invertebrates, altering the food web, and impacting food sources for native trout and other fish, while offering them little nutritional value in return. It also impacts water by altering natural cycles, such as the nitrogen cycle.


Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).

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