New Zealand Mudsnail (Potamopyrgus antipodarum)
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Originally from New Zealand, this tiny snail has spread into many parts of Europe, Asia, Australia and North America. Its small size and the presence of an operculum, a small cover that can be used to close the shell opening, allow this animal to survive out of water and hitchhike unnoticed on a variety of things, from recreational equipment such as waders and boots, to wildlife feet or fur. All known populations in the PNW are composed of female clones, allowing a single snail to start an entire population. Mudsnails have no egg or larval stage; live young develop directly to adults.
New Zealand Mudsnail photo courtesy of Oregon Seagrant.
Population densities in Europe have been recorded as high as an astonishing 800,000 per square meter. At such high densities, it can consume most of the primary production in a stream, out-compete other invertebrates, and change the nitrogen cycle and the ecosystem trophic structure. The operculum also allows the snail to pass alive and undigested through the gut of predators, which means that they not only provide no nutrition for their predators, but they may also be excreted in new locations, where they can then start new populations. Their presence is sometimes considered an indicator of poor water quality.
Mudsnails resemble species of our native snails, but the very small size of adults (3-6 mm) and the presence of an operculum help identify them.
Status in the Pacific Northwest: First found in the PNW in Snake River near Hagarman ID in 1987, within 2 years they became the dominant snail in that area. They have since spread to some areas of WA, OR, ID, MT, and WY, as well as southwestern states of AZ and CA. Presence in WA and OR is still somewhat limited.
What can you do? Once mudsnails are established, there is no way to eradicate them without damaging other parts of the ecosystem, so prevention of the spread is very important. Clean boots and field gear with a stiff brush before leaving a site to ensure all traces of mud and sand are removed. Dry your boots and other field gear for 48 hours to remove all traces of dampness before using them again. If you are in the field often, if possible, have several changes of boots to allow drying between uses. When cleaning fish from infested waters, because mudsnails in the digestive tract may still be viable, insure the internal organs are disposed of where they will not have contact with uninfested water.
If you think you have found mudsnails, save 5-10 individuals in a bag with a bit of water, and go to http://www.esg.montana.edu/aim/mollusca/nzms to confirm identification. If the identification appears to be correct, save the samples and contact:
In Washington: 1-360-902-2700 (ANS Coordinator)
In Oregon: 1-866 INVADER (hotline)
In Idaho: 1-208-332-8686 (ANS Coordinator)
In Alaska: 1-877-INVASIVE (hotline)
National Management Plan: New Zealand Mudsnail
Preventing Mudsnail Spread Through Field Gear (brochure)