New Zealand Mudsnail
The New Zealand mudsnail is an invasive species that damages the ecosystem of Colorado.
About This Species
New Zealand mudsnails are small aquatic snails not native to Colorado. They were first discovered in North America in the late 1980’s in the Snake River, Idaho and Madison River, Montana. They are voracious eaters that reproduce rapidly, eating much of the available food. This negatively affects aquatic insect larvae, native snails, as well as fish populations. They are able to pass through a fish's digestive system unharmed, leaving the fish malnourished.
New Zealand Mudsnail in Colorado
New Zealand mudsnails are spread into new river systems primarily by humans, although they can be carried on the feet of dogs and wildlife. Anglers, boaters, researchers and others can carry NZMS to non-infested locations on their boots and gear. They can reproduce sexually or asexually, so just one snail can start an entirely new population. Once they have invaded, they are nearly impossible to contain because they are highly resilient. The snails can survive several days out of water, in a wide range of temperatures, and for days up to weeks on damp to wet materials. They can even pass unscathed through the digestive tracts of fish.
- Thoroughly wash waders, boots, tack, and other fishing gear. Wash by soaking in a solution of 50% water and 50% bleach (or other cleaning solution) for five minutes, rinse in clean water, and air dry out of direct sunlight. Freezing overnight also kills the snails.
- Remove all sediment and vegetation from boats, trailers, and fishing gear when moving between waters. Drain boats, equipment, coolers, live bait wells and any holder of water.
- Do not transport any fish from one body of water to another. It is illegal in Colorado to move and stock live fish without a special license.
Infected Waters
Colorado Parks and Wildlife is monitoring the state’s waters for the introduction of an aggressive invasive species, the New Zealand Mudsnail.
Waters Positive for New Zealand Mudsnail
Find out moreReport a Sighting
If you have seen or suspect you have seen a New Zealand mudsnail, please report it using this form.
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Physical Characteristics
Size
New Zealand Mudsnails range in size from a grain of sand to 1/8 inch in length and are black or brown in color.
Shell
The shell has about 5 ½ spirals. If the shell is held tip up with the opening toward you, the opening is on the right. There is an attached operculum (cover) which can close off the opening.
Commonly Found
They are native to fresh waters of New Zealand.
Range
The snail inhabits a wide range of aquatic habitats, including streams and reservoirs in the western U.S. In Colorado, the mud snail has been discovered in Boulder Creek and in the South Platte River in Eleven Mile Canyon.
Habitat
Found in freshwater, brackish, or saline waters with almost any substrate. Populations in saline conditions produce fewer offspring and grow more slowly. Also tolerates a wide range of temperatures, ranging from near freezing to 82° F.
Diet
Mud snails consume food in cobble or gravel substrates or on aquatic vegetation, competing with native invertebrates for space and food resources. Reduction in native insect species diversity or abundance diminishes the availability of this critical resource for fish such as trout.
Reproduction
New Zealand mud snails are capable of rapid population growth. The species reproduces asexually, giving birth to well-developed clones. Just one snail can start a whole new colony in a stream or river, by multiplying in astounding numbers, and completely covering stream bottoms.
Threats to Species
New Zealand Mud Snails compete with native invertebrates, including native mollusks, for space and food resources. They may reduce the availability of native invertebrate prey for fish- particularly mayflies, caddisflies, and chironomids. They are not a viable food source themselves- their hard shell allows them to pass through a fish gut unharmed. New Zealand mud snails are not a viable food source for native fish and yield as little as 2% of their nutritional value when eaten by trout.