Minnesota Crustaceans

Rathke’s woodlouse is a non-native isopod. It is native to central Europe, was introduced into North America, and now occurs from Newfoundland south to Tennessee and west to South Dakota. It is not uncommon in Minnesota. It is found in places with at least some dampness, including on rotting logs; under logs, stones, and boards; and in woodsheds and greenhouses. It is mostly a scavenger, eating plant and animal organic matter, but sometimes also feeds on living plants.

Unlike pill woodlice (Family Armadillidae), Rathke’s woodlouse cannot roll into a ball.

Rusty crayfish (Orconectes rusticus) is a medium- to large-sized freshwater crustacean. It is native to Michigan, Ohio, and Kentucky. It is used extensively by fishermen as bait, and is sold as an aquarium pet. Unused bait and release of aquarium pets have resulted in the introduction of this species across the United States. It is considered invasive outside of its native range.

Rusty crayfish are extremely aggressive. They out-compete and eventually eliminating native crayfish species when introduced into a new site. Juveniles have a higher metabolic rate, eat twice as much, and develop much faster than native crayfish species of similar size.

Rusty crayfish is identified by a rust-colored spot on each side of its upper shell; a rust-colored stripe on the uppers side of its abdomen; and very large claws with an S-shaped movable finger.

Virile crayfish (Orconectes virilis) is a medium- to large-sized freshwater crustacean. It is widespread and abundant across North America. It is native to central United States and Canada, from Quebec to Tennessee in the east, to Alberta and Colorado in the west. It is introduced and considered invasive outside of its native range from coast to coast.

Virile crayfish prefer streams with rocky bottoms, moderate flow and turbidity, abundant cover, and stable water levels. They often use rocks, logs, or other organic debris as cover. They occasionally dig burrows into muddy banks, especially when water levels are low. To survive the winter, they migrate to deeper water that does not completely freeze and they become inactive.

Virile crayfish are identified by the dappled, olive-brown body with pairs of dark brown splotches on the abdomen; the shape of the shield (carapace) covering the front part of the body; and the broadly flattened, usually bluish claws.