New Zealand Mud Snails

What do New Zealand Mudsnails look like?


New Zealand Mudsnails are small (3 to 6 mm or 1/8 inch) snails that have brown or black cone-shaped shells with 5 whorls.

Why are New Zealand Mudsnails considered to be a nuisance?

Densities & Competition with Native Species – This snail has the ability to reproduce quickly and mass in high densities. When snails become as dense as one-half million per meter square, this has been a cause for concern in western streams. Because the West is known for its great trout fishing, there is concern that the mudsnails will impact the food chain of native trout and alter the physical characteristics of the streams themselves. Research is needed to determine the impacts of large populations of mudsnails on the native fauna, such as aquatic insects and native snails, and on any changes in the physical environment.


Ability to Survive in Variable Conditions – The rapid spread of the mudsnail throughout Putah Creek may have been assisted by human transport. Mudsnails are able to withstand dessication, a variety of temperature regimes, and are small enough that many types of water users (anglers, swimmers, picnicers, pets) could inadvertently be the mechanism for interbasin transfer of this nuisance species.

What is the New Zealand Mudsnail’s potential to spread elsewhere in U.S.?

There is great concern about this hitchhiker’s ability to spread because of its asexual reproduction and its ability to survive in harsh conditions. Because the mudsnails reproduce asexually, it only takes one individual to become introduced into new water to make an impact. Also, the mudsnails can readily attach themselves to boots and waders. So anglers must be vigilant in checking their gear and ensuring that it is free of mud and any noticeable snails.

How can I prevent the spread of New Zealand Mudsnails?

1.Soak your boots, waders and gear in equal parts water and Formula 409 degreaser/disinfectant . . . NOT regular Formula 409!

2.Or Soak your boots, waders and gear in 3/4 tsp (3.8 grams) of 99% Copper Sulfate Pentahydrate in 1 gal.of water

3.Or Freeze your boots, waders and gear solid. This might take 6-12 hours or more.

4.Or Completely dry your boots, waders and gear. This isn’t as easy as it sounds, a slight damp spot under the insole can harbor live snails for over a month. Heat will assist in killing snails during drying.

5.Or Consider dedicating a set of wading gear to waters known to harbor New Zealand Mud Snails.

To learn more, you can read the Official Report by the DFG:
Controlling the Spread of New Zealand Mud Snails on Wading Gear

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