The non-native and potentially invasive signal crayfish has appeared for the first time in Minnesota, prompting the state to warn that they are illegal without a permit.

Officials confiscated 10 signal crayfish that a commercial harvester found in Lake Winona, near Alexandria, Minn., in September and October. The harvester contacted the state Department of Natural Resources (DNR) and wanted to remain anonymous, said Don Eaton, a DNR aquatic invertebrate biologist.

All of the crayfish were adults.

"What we're hoping, of course, is we have all of them," Eaton said. "There was no sign that they reproduced yet."

Minnesota is home to five smaller native species of crayfish — three of them common, including the virile crayfish, the calico crayfish and the devil crayfish.

This signal crayfish, a native of the Pacific Northwest, can grow up to 7 inches long and weigh as much as 4 ounces — about three times larger than native Minnesota crayfish, according to the DNR. They also live longer, about nine years or more, and are sold in the pet trade.

They eat a range of aquatic plants, fish eggs, other crayfish and native invertebrates. The underside of their claws is bright red, Eaton said.

He said the DNR has no idea how signal crayfish arrived in Minnesota. The closest previously known population is in western Montana.

It's not the first non-native crayfish that has appeared in Minnesota. The rusty crayfish, native to the Ohio River basin, is now widespread in the eastern half of the state, Eaton said.

Anyone who finds a signal crayfish is asked to photograph it, identify the location and collect the species. The information can be submitted at the EDDMapS website or to the local DNR.