Invasive Species of Concern

New Zealand Mudsnail
Potamopyrgus antipodarum

caulerpa, noaa fisheries photo

New Zealand Mudsnail
USGS photo

The New Zealand mudsnail (Potamopyrgus antipodarum, NZMS) is spreading rapidly in the western United States with several new populations being discovered every year. The snails first appeared near Hagerman Idaho, and were documented by S.W. Taylor in 1987. The snails are small, only 5-6 mm in length. An expert in snail identification should be consulted for specimen identification purposes.

This species, which is indigenous to New Zealand and its adjacent islands, is now found in Australia and is widespread in Europe where it was misidentified for many decades. The introduced populations of these tiny snails (up to 6 mm) are mostly all female and the snails are live bearers.

Unfortunately, studies have shown fish derive little or no energy value from eating snails because the snails are capable of passing through the fish's digestive system alive and intact. The exact time of arrival and source of the snails are unknown but it has been speculated that they arrived from the commercial movement of aquaculture products such as trout eggs or live fish.

A database established on the New Zealand Mudsnail in the Western USA web site is being used to track new populations and keep people informed about the latest research. Range expansion of the mudsnail has been unwittingly hastened by anglers, hunters, and field personnel—in other words, people who frequently move from one watershed to the next, hauling wet waders, nets, and other gear with them.

NZMS can be moved by: Recreational watercraft and trailers, Fish hatcheries and associated stocking operations, Recreational water users, Natural resource management activities, Commercial shipping, Sand/gravel mining, extraction, and dredging, Aquatic plant trade and collections, Transport of fish, wildlife and livestock, Firefighting, and Transport by water flow.