The New Zealand mudsnail is another invasive species now living in the Duluth-Superior Harbor and St. Louis River estuary. Natural resource officials from Minnesota and Wisconsin urging anglers and other river users to take steps to prevent accidentally spreading mudsnails.

Over 100 snails were collected last fall by a research team from the EPA’s Mid-Continent Ecology Division in Duluth. The team was conducting a survey as part of a project designed to look for new invaders in Great Lakes harbors. This is the first finding of the tiny snail in Minnesota and Wisconsin waters.

A contract research scientist who was part of the team identified the New Zealand mudsnail among the samples. Following confirmation of the mudsnail’s identity, the EPA disclosed preliminary results of the survey earlier this month.

"I kind of expected to find them," said Igor Grigorovich of Wilson Environmental Laboratories, Inc., the contract scientist who was also first to find the species in Lake Superior near Thunder Bay, Ontario, in 2001. "The St. Louis River estuary is a more suitable habitat for this snail species than Lake Superior, because it’s not as cold."

"They possess a thicker and more opaque shell," Grigorovich said. "The Thunder Bay snails are semi-transparent, probably as a result of low calcium content in Lake Superior water."

New Zealand mudsnails cause concern because their sheer numbers can disrupt the ecosystem.

"They have adapted so well in Western rivers that they have pushed out almost all of the native insects, snails, and other invertebrates that are important food for fish," said Doug Jensen, aquatic invasive species program coordinator for Minnesota Sea Grant. "More than 700,000 snails per square meter cover the bottoms of some rivers. That’s like having 585,000 snails in your bathtub!"

Another concern is that they can spread easily on aquatic plants, waders, and other gear used in infested waters. They are able to close their shells, allowing them to survive out of water for days. Also, they can start new infestations because they can reproduce without mating, essentially cloning themselves.

One snail and its offspring can form hundreds of thousands of clones per year. Native fish and wildfowl eat them, but because they are so prolific, nothing seems to control infestations in North America.

New Zealand mudsnails are tiny mollusks (about the size of a peppercorn) native to New Zealand. Their spiral-shaped shells are usually dark gray or dark brown to light brown with a right-handed coiling pattern and 5-6 whorls. Some native snails look similar to the mudsnail, which makes identification difficult.

They were first found in the U.S. in Idaho’s Snake River in 1987. It is believed they were accidentally introduced with stocked rainbow trout. The snails have been found in other Rocky Mountain trout streams, apparently spread by anglers. Researchers suspect they arrived in the Great Lakes via ship ballast water.

The DNRs in both Wisconsin and Minnesota are working to designate the New Zealand mudsnail as a prohibited invasive species. The designation means it will be illegal to import, transport, possess, and place mudsnails into other waters in the state, as it is with other prohibited species such as zebra mussels. An exception is if a person is bringing the mudsnail to the DNR for identification or reporting purposes.