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Invasive Species: New Zealand Mudsnail

New Zealand Mudsnail

(Potamopyrgus antipodarum)
*Detected in Michigan*



  • Small snail, averaging 1/8 inch long.
  • Right-side opening with 5-6 whorls on shell.
  • Shells vary from light brown to black.
  • Difficult to identify.

New Zealand mudsnails
New Zealand mudsnails are small and brown to black in color. Photo courtesy of Michigan EGLE.

new Zealand mud snail
Shells have 5-6 whorls and open on the right side. Photo courtesy of University of Colorado Museum of Natural History.


If possible, please take one or more photos of the invasive species you are reporting. Also make note of the location, date and time of the observation. This will aid in verification of your report. You may be asked to provide your name and contact information if follow-up is needed.


Habitat: New Zealand mud snails can tolerate a wide variety of habitats, including reservoirs, estuaries, rivers, and lakes. They are most prolific in water bodies with a constant temperature and flow, but are highly adaptable.

Native Range: New Zealand.

U.S. Distribution: Western United States, Great Lakes and the Chesapeake Bay.

Michigan Distribution: New Zealand mudsnail populations are present in the Au Sable, Boardman, Grass, Pere Marquette, Pine and Upper Manistee rivers in Michigan.

Michigan Status: New Zealand mudsnails are prohibited in Michigan.

Local Concern: This mudsnail reproduces by cloning, which means females develop complete embryos without fertilization. In a matter of one year, a single female could result in a colony of 40 million snails. When large colonies of mudsnails are present, food for other stream invertebrate populations can become scarce. Fish that feed on native invertebrates like mayflies and caddisflies may find it more difficult to forage in rivers invaded by New Zealand mudsnails. Fish will consume New Zealand mudsnails, but due to the snail’s thick shell, equipped with a tightly closing “hatch” called the operculum, they are difficult for fish to digest, offer the fish little nutritional value and can be excreted alive. Substituting mudsnails for native food sources can reduce the growth, condition and ultimately the abundance of key sport fish including trout.

Means of Introduction or Spread: New Zealand mudsnails can be transported on boats, anchors and fishing gear such as waders and nets. Because of their small size and ability to survive out of water for several days, it is important to carefully decontaminate boats and gear between uses. 

What you can do:

Always Clean, Drain, and Dry your waders, boots, boats and other gear between trips or before moving to a new body of water. Take extra precaution in areas with known or suspected didymo or New Zealand mudsnail infestations. In addition to removing debris and mud, the State of Michigan recommends using a chemical disinfectant to achieve maximum decontamination for didymo and New Zealand mudsnail. Possible disinfectants with documented effectiveness for these species include:

  • Products such as Formula 409® Antibacterial All-Purpose Cleaner applied to waders and gear.
  • Bleach: Apply a solution of  ½ cup (4 fluid ounces) bleach to 5 gallons of water and let stand for 20 minutes.
  • Virkon Aquatic: Apply a solution of 20 grams per liter of water and let stand for 20 minutes (see manufacturer’s label for additional guidance).

Any chemical disinfectants should be applied to waders and gear on land, at a reasonable distance from the water, to avoid accidental discharge into surface waters. 

These methods work for didymo, New Zealand mudsnails and most other aquatic invasive species.

Helpful Tips:

  • Avoid visiting multiple rivers in a single day.
  • Plan time to decontaminate between trips.
  • Designate specific gear, especially porous items like nets or rope, for use only in infested waters.