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New Zealand Mudsnail - Potamopyrgus antipodarum

Aquatic Invasive Species
Exotic Species (not native to Montana)

Global Rank: G5
State Rank: SNA
* (see State Rank Reason below)

Agency Status


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State Rank Reason (see State Rank above)
A conservation status rank is not applicable because this species is not a suitable target for conservation activities as a result of being exotic or introduced.
General Description
New Zealand Mudsnail (NZMS) is a small snail (4-6 mm) with a dextral (right-handed coiling), elongated shell with 5-6 whorls separated by deep grooves. It is generally dark brown to grey in color. This is an introduced species to MT with a stable or expanding distribution in the Missouri, Madison, Yellowstone, and Bighorn Rivers. It is not known in Montana west of the continental divide. In Montana this species was first discovered in the Madison River above Hebgen Reservoir in 1995 (Gustafson pers. comm.). However, the very large population present at that time indicataes that the introduction was a few years earlier. It is a native of New Zealand, but long established in Australia and Europe. This species has been known in North America since 1987 in the Snake River basin of Idaho

Diagnostic Characteristics
Taxonomically, New Zealand mud snails are in the snail family Hydrobiidae. Hydrobiids can be distinguished from other aquatic snail families by having dextral (opening to the right with the spire pointing away from you) shells with an operculum (a hard calcareous flat that can seal the opening of the shell). New Zealand mud snails are small (~ 2-6 mm) and generally dark colored

Range Comments
Native Range: The freshwater streams and lakes of New Zealand and adjacent small islands; it is naturalized in Australia and Europe (Hall et al. 2003).

Global Range: (>2,500,000 square km (greater than 1,000,000 square miles)) Introduced to Europe in the 1800's where it is now widespread. Introduced into the Snake River system (Idaho) in North America (first appeared in 1987). Since then it has spread, from a second introduction to nearly a dozen sites in Lake Ontario (Zaranko et al., 1997). Kerans et al. (2005) list it from Idaho, Great Lakes, California, Colorado, Wyoming and Montana.
The NZMS was first discovered in the middle portion of the Snake River in Idaho in 1987. By 1995, the mudsnail had reached the Madison River in Montana, and into Yellowstone National Park the following year (Wyoming). It is also established in Minidoka National Wildlife Refuge, Idaho (USFWS 2005). Populations were discovered near the mouth of the Columbia River in Oregon in 1997, and the Owens River in California. Since then, this species is becoming very widespread in California. This species became established in the lower Columbia River, Washington about 1999 (M. Sytsma, pers. comm.) and in the Colorado River in northern Arizona by 2002 and continues to spread (Cross et al 2010). In Utah, the first mudsnails were found about 2001 and have since been found in the Green River and many others. In 2004, mudsnails were found in small Colorado creek near Boulder (P. Walker, pers. comm.). Since the early 2000's, high NZMS densities in the in the Missouri and Madison Rivers have declined, but are more recently building their populations back (Stagliano 2017).

Summary of Observations Submitted for Montana
Number of Observations: 5

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

Potamopyrgus antipodarum can survive passage through the guts of fish and may be transported by these animals (Bruce 2006). Throughout Montana, it has been transported to different waterbodies on the felt soles of fishermen’s wading boots (ANS 2007). It can also float by itself or on mats of Cladophora spp., and move 60 m upstream in 3 months through positive rheotactic behavior (Zaranko et al. 1997). It can respond to chemical stimuli in the water, including the odor of predatory fish, which causes it to migrate to the undersides of rocks to avoid predation (Levri 1998).

Means of Introduction or Expansion: 1) Fish hatcheries and associated stocking operations, 2) Recreational watercraft and trailers, 3) Recreational water users: Particularly when embedded in mud or attached to plant debris, NZ mudsnails may be transported on fishing gear, on waders and boots, swimsuits and swimming toys and even by hunting dogs and horses, 4) Sand/gravel mining, extraction, and dredging: Any waterway operations that remove and transport mud, sand, and other bottom materials from areas with NZ mudsnails can serve as a vector for new introductions, 5) Aquatic plant trade and collections (ANS 2007). Potamopyrgus antipodarum was most likely introduced to the Great Lakes in ships from Europe, where there are nonindigenous populations (Levri et al. 2007, Zaranko et al. 1997) or in the water of live gamefish shipped from infested waters to western rivers in the United States.

New Zealand mud snails appear to prefer flowing water habitats with stable flows. Springs, spring creeks, and river sections downstream from dams are all places that they thrive in. They can survive in cool lakes with suitable habitat. They are most typically found on larger cobble substrates or on pieces of wood.

Food Habits
The NZMS is a nocturnal grazer, feeding on plant and animal detritus, epiphytic and periphytic algae, sediments and diatoms largely on cobbles or submerged woody debris.

The NZMS is a nocturnal grazer, feeding on plant and animal detritus, epiphytic and periphytic algae, sediments and diatoms (Zaranko et al. 1997, USGS 2017).
The snail tolerates siltation, thrives in disturbed watersheds, and benefits from high nutrient flows allowing for filamentous green algae growth. It occurs amongst macrophytes and prefers littoral zones in lakes or slow streams with silt and organic matter substrates, but tolerates high flow environments where it can burrow into the sediment (Collier et al. 1998, Death et al. 2003, Holomuzki and Biggs 2000, Richards et al. 2001, Zaranko et al. 1997).

Reproductive Characteristics
Potamopyrgus antipodarum is ovoviviparous and parthenogenic. Native populations in New Zealand consist of diploid sexual and triploid parthenogenically cloned females, as well as sexually functional males (less than 5% of the total population). One snail produces approximately 230 young per year. Reproduction occurs in spring and summer, and the life cycle is annual (Gerard et al. 2003, Hall et al. 2003). All introduced populations in North America are clonal, consisting of genetically identical females.

NZMS have great potential for wide-spread colonization because they have a broad environmental tolerance. Although the species occurs in a wide range of aquatic habitat types, including diverse ranges of temperature, osmotic concentrations, flows, substrates and disturbance regimes, clonal lineages may have either narrow or broad ecological tolerances. Likely to find all shallower waters (<50 m depth) as suitable habitat. High spread potential (USEPA 2008). Abundant populations of introduced P. antipodarum may outcompete other grazers and inhibit colonization by other macroinvertebrates (Kerans et al. 2005).

Many times a newly discovered population of NZ mudsnails may be in a river or lake where chemical eradication will not be feasible and physical eradication difficult. This would be the case with large rivers or lakes where it is impossible to isolate the invader and treatment would be difficult to contain. In other situations the invader may occupy too large an area or other ecological or political restraints may rule. Areas where eradication may be possible include small lakes and ponds, waterbodies that can be temporarily hydrologically separated (e.g., curtain, wall), irrigation canals, and fish hatcheries.

Threats or Limiting Factors
Threats to the NZMS are minimal, other than reservoir drawdowns and river dewatering which will leave the snails prone to desiccation. Although a discrepancy exists when comparing temperature tolerance limits of North American and New Zealand populations. North American populations are generally adapted to warmer temperature regimes than their New Zealand counterparts.

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Citation for data on this website:
New Zealand Mudsnail — Potamopyrgus antipodarum.  Montana Field Guide.  .  Retrieved on , from