New Zealand mudsnails

Why are they a problem?

New Zealand mudsnails are a non-native species that have no natural predators, parasites, or diseases to control their population size in North America. They are hardy, adaptable animals that can easily be transported to new areas by people, pets, wildlife, and equipment. At this time we cannot predict just how large of a problem they will become in the Puget Sound region, but we do know that once they are present in a stream or lake, it is impossible to get rid of them without seriously harming native species present.

These snails threaten the health and stability of aquatic ecosystems because they crowd out native species—they reproduce quickly and have reached densities of over 400,000 snails per square meter in parts of the US. They have little or no nutritional value to fish or other species; however, they may be consumed instead of other animals that do have nutritional value.

Some studies have indicated that New Zealand mudsnails can alter the chemistry of streams, disrupt the natural food chain, and drive out native stream insects. Natural resource agencies throughout the West are concerned that these animals could further harm threatened and endangered salmon runs.

In Washington, these mollusks are a “prohibited” species and their transport is prohibited by law (RCW 77.12.010). In other words, it is illegal even to carry them accidentally via muddy boots, tires, or fishing gear.

What should you do?

Keep in mind where these snails have been found to date, and avoid going into the water or damp, muddy places in those areas. If you do enter the water or adjacent damp areas, then clean your boots and check carefully afterwards to make sure you are not carrying them:

• Don’t move damp or muddy clothing and gear between water bodies. Hiking boots, sandals, wading gear, bike tires, pets, fishing gear, and nets can all provide attachment places for mudsnails to hitch a ride to a new home.
• Clean your gear at the site. At a minimum, wash thoroughly, brush, and inspect any gear (or pets) that went near the water. Be sure to remove all mud, twigs, animals, and debris that are caught on your gear or your pet’s fur. A stiff brush works well for scrubbing your gear, followed by a thorough rinse with clean water.
• Completely dry your clothes and gear. Put them in a dryer on high heat for at least 2 hours, or air dry for at least 48 hours. New Zealand mudsnails can survive in damp conditions for days and sometimes even weeks.

New Zealand mudsnails can lodge in small crevices and folds of field gear, equipment, boats, and heavy equipment. Felt-soled waders have particularly been targeted as good spots for the snails to hitch rides, and some states are considering banning their use in fresh water bodies.

If you visit streams, lakes, rivers, or wetlands frequently, then it is recommended you retire any felt-soled waders or wading boots and replace with rubber-soled boots. Then consult one or more of the following guides that describe various decontamination procedures such as freezing, hot water treatment, and chemical disinfection:

• Invasive Species Management Protocols, by Washington Department of Fish and Wildlife
• Minimizing the Spread of Invasive Species, by Washington Department of Ecology