New Zealand Mudsnails

The New Zealand mudsnail, Potamopyrgus antipodarum, is an aquatic invasive species that was first found in the United States in Idaho in the 1987, and has since spread to every Western state except New Mexico. They appeared in California in the late 1990’s in the Owens River, and were found in southern California in Malibu Creek in 2005 and in Piru Creek in the Santa Clara River watershed in 2006. Since their discovery in Malibu Creek, they have spread to several streams in the Santa Monica Mountains.

New Zealand mudsnails are tiny, with adults only reaching 3-5 mm and juveniles even smaller, about the size of a grain of sand. They are usually light to dark brown, and may appear black when wet. They have conical shells that have five, or sometimes six whorls.

New Zealand mudsnails reproduce clonally and bear live young. Broods of up to 120 can be produced three times per year in warm climates, and a single female and her offspring are capable of yielding 40 million individuals in a year.

We believe they compete with native invertebrates for food and habitat though research is currently underway. What is known is that they reach huge densities. Over 750,000 individuals per square meter have been recorded in the Yellowstone River. As they provide little in the way of food value, they may have detrimental effects on fish and wildlife. They have wide ranging temperature and salinity tolerances, and can survive for several days out of water under moist conditions.

Taken together, their small size, dark coloration, and ability to stick to things makes them excellent at invading new systems. They can hitch a ride on fishing gear, sampling equipment, shoes (hiding in the treads and under the laces), and clothes, as well as on the fur of dogs and horses. We know of no way to get rid of them once they invade a river system, other than drastic dewatering or poisoning. Researchers are investigating options for biological control.