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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, and in 2009, in the Wilmington drain near the San Gabriel River estuary. Since their discovery in Malibu Creek, they have spread to several streams in the Santa Monica Mountains. In 2016 and 2017, they were found in North Fork Matilija Creek and the Ventura River mainstem. 

Photo by Ken Davis
Photo by Ken Davis
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 on a leaf. Photo by S. Drill
New Zealand mudsnails on a leaf. Photo by S. Drill
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.

NZMS on a boot. Photo by Ken Davis
NZMS on a boot. Photo by Ken Davis
The best way to manage New Zealand mudsnails and other invasive species is to try and prevent them from spreading. Stay out of infected streams and do NOT to go from one stream to another in wet gear. If you need to go into an infected stream, consider having dedicated clothes and gear that you don’t wear anywhere else. Scrub all gear with a stiff brush before you leave an infected site; mudsnails are experts at hiding, so you can’t trust a visual inspection. Let all gear dry completely between visits, or freeze for a minimum of six hours between uses.

More Information

USGS Map of current New Zealand Mudsnail distribution in the US

 

UCCE New Zealand Mudnsnail Fact Sheet


Ver un video en español

 

CDFW Invasive Species Program

 

Protect Your Waters: Stop Aquatic Hitchhikers

 

Education about the problems caused by releasing unwanted pets and plants. http://www.habitattitude.net/