The New Zealand mudsnail, a mollusk, is native only to New Zealand. It was first discovered in North America in the 1980s in the Snake, Madison and Idaho rivers, but no one knows how it arrived there. This small, invasive creature quickly spread to Yellowstone National Park. From there it spread to many other bodies of water, streams and rivers across the west.
The mudsnail invades new habitat when it becomes attached to fishing gear, or boats, or trailers, or even fish and bait, and then comes off in the next stream or river where these things are used or discarded. Mudsnails consume aquatic vegetation, upsetting the balance of the aquatic environment.
How to Identify the New Zealand Mudsnail
- The mudsnail is an average of 1/8 of an inch long (but can be as small as a grain of sand) and has a gray-brown cone shaped shell that consists of five whirls.
- They can live in all kinds of waters—from silted river bottoms to clear mountain streams.
- The mudsnail can tolerate temperatures from 32ºF. to 77ºF., but prefer temperatures of about 66ºF.
- They reproduce asexually; it only takes ONE to start a whole new population!
- Mudsnails can survive out of water for several days, so it's easy to see how they can move about and survive on recreational gear.
See the mudsnail fact sheet 
for more information.
Help Stop the New Zealand Mudsnail
Densities of over 500,000 per square yard have been found in Yellowstone National Park! Because of this mollusk's lack of predators (it's controlled naturally by a parasite in New Zealand), it often has a great advantage over native species and in many cases can overwhelm native plants and animals. Biological invasions can change the way we use and enjoy our natural resources, and these changes are often not for the better. Trout and other recreational fisheries could be reduced forever.
Four Options to Keep Your Angling Gear Free of Invaders
Keep all angling gear free of mud, plants, and organic debris in between each and every use. Unknowingly moving a species from one body of water to another, even within different stretches of the same river, can start a domino effect of invasion, causing irreversible ecological damage. It is especially important to keep waders clean.
Anglers should scrub the bottom of boots or waders with a brush and remove all mud, plants, and organic materials in between each and every use. Anglers should then perform ONE of the following options before going into the next body of water:
OPTION 1
Submerge waders and gear in a large tub filled with a mixture of 6 ounces per gallon quaternary ammonia based institutional cleaner (such as Super HDQ Neutral) and water for at least 10 minutes, scrubbing debris from the gear, and visually inspecting the gear for snails before rinsing. Follow all precautionary label instructions! Rinse water must be from a New Zealand mudsnail-free source (to avoid re-infection), and the chemical bath must be properly disposed of, away from the water body.
OPTION 2
Spray or soak waders and gear with 140º Fahrenheit water for at least 10 minutes.
OPTION 3
Dry your waders and equipment completely for a minimum of 10 days in between each use (remember that mudsnails can survive several days out of water).
OPTION 4
Place waders and boots in a freezer overnight between use.
More Information
News Releases
Report Sightings!
Timely and accurate identification is very important in dealing with invasive species. To help the Colorado Parks and Wildlife quickly identify new populations of this unwanted species please report any sightings to Elizabeth Brown, Invasive Species Coordinator, 303-291-7362