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.

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. Help control the spread:

• Rinse mud and debris from waders and gear after each use, before moving on to the next stop.

• Take a hot water bath (120ºF) for several minutes.

• Let equipment dry for several days between uses. Remember that mudsnails can survive several days out of water.

• Dry heat will kill them. Spray them with soapy water and leave them in the hot sun for several hours. (The soap breaks down the mucous that helps them hold on to moisture.)

Timely and accurate identification is very important in dealing with invasive species. To help the Colorado Division of Wildlife quickly identify new populations of this unwanted species please report any sightings to Elizabeth Brown, Invasive Species Coordinator, 303-291-7362.