This species was originally
endemic to
New Zealand where it lives in freshwater streams and lakes in New Zealand and adjacent small islands. and Iraq), and North America (USA and Canada It does not occur in Iceland, Albania or the former Yugoslavia. Countries where it is found include: •
Great Britain since 1859 •
Ireland •
Germany •
Poland • Western Baltic Sea since 1887 • Russia • Azov
Black Sea region, since 1951, • Catalonia in Spain, since 1952 •
Slovakia, since 1986 • Greece, since November 2007
Distribution within the United States First detected in the
United States in
Idaho's
Snake River in 1987, the mudsnail has since spread to the
Madison River,
Firehole River, and other watercourses around
Yellowstone National Park; samples have been discovered throughout the western United States. Fish populations then suffer because the native snails and insects are their main food source. Mudsnails are impressively resilient. A snail can live for 24 hours without water. They can however survive for up to 50 days on a damp surface, giving them ample time to be transferred from one body of water to another on fishing gear. The snails may even survive passing through the digestive systems of fish and birds. The snails grow to a smaller size in the U.S. than in their native habitat, reaching 6 mm ( in) at most in parts of Idaho, but can be much smaller making them easy to overlook when cleaning fishing gear. Clonal species like the New Zealand mudsnail can often develop clonal lines with quite diverse appearances, called
morphs. Until 2005, all the snails found in the western states of the U.S. were believed to be from a single line. However a second morph has been identified in Idaho's Snake River. It grows to a similar size but has a distinctive appearance. (It has been nicknamed the salt-and-pepper mudsnail due to the final whorl being lighter than the rest of the shell.) This morph has apparently been present in the area for several years before being identified correctly as a distinct morph of
Potamopyrgus antipodarum. It dominates the typical morph where they overlap, and has a much higher prevalence of males. In 1991, the New Zealand mudsnail was discovered in
Lake Ontario, and has now been found in four of the five
Great Lakes. In 2005 and 2006, it was found to be widespread in Lake Erie. By 2006 it had spread to
Duluth-Superior Harbour and the freshwater estuary of the
Saint Louis River. It was found to be inhabiting
Lake Michigan, after scientists took water
samples in early summer of 2008. The snails in the Great Lakes represent a different line from those found in western states, and were probably introduced indirectly through Europe. A heavy cold snap in 2013, combined with a drawdown in water level in preparation, was roughly estimated to have killed 40–60% of the mudsnail population. Other known locations include the Long Beach peninsula, Kelsey Creek (King County), Thornton Creek (King County), and
Lake Washington. In 2010, the
Los Angeles Times reported that the New Zealand mudsnail had infested watersheds in the
Santa Monica Mountains, posing serious threats to native species and complicating efforts to improve stream-water quality for the endangered Southern California
Distinct Population Segment of
steelhead. According to the article, the snails have expanded "from the first confirmed sample in Medea Creek in
Agoura Hills to nearly 30 other stream sites in four years." Researchers at the Santa Monica Bay Restoration Commission believe that the snails' expansion may have been expedited after the mollusks traveled from stream to stream on the gear of contractors and volunteers. In Colorado, Boulder Creek and Dry Creek have infestations of New Zealand mudsnails. The snails have been present in Boulder Creek since 2004 and were discovered in Dry Creek in September 2010. Access to both creeks has been closed to help avoid spread of the snails. In the summer of 2015 an industrial-scale wetland rehabilitation project was undertaken in northeast Boulder to rid the area of a mud snail infestation. ==Ecology==