The northern crayfish grows to be 120 mm long. It has two long antennae that help it feel for food and enemies. Crayfish have 4 pairs of walking legs and 1 pair of grasping claws or pincers. The males have larger pincers than the females. The crayfish head and body are covered in a shell that is brownish to rusty-red in colour.

A crayfish will eat almost anything living or dead. It eats both plants and animals. It picks up bits of food with the claws on its walking legs and can tear up larger bits of food with its large pincers. Crayfish can catch some live animals to eat, but most of their food is plants or dead animals that they find.

Crayfish live in rivers, steams, lakes and ponds. They prefer to live where there is a rocky bottom.

Crayfish are eaten by many fishes, amphibians, birds and mammals. They hide under large rocks during the day. They come out mostly after dark to look for food. If they sense danger, crayfish can shoot backward quickly by flipping their tails under their body. When the crayfish molts its old armoured shell it must remain in hiding until their new shell hardens. If a crayfish loses a pincer, it can regrow a new one.

Crayfish eggs are laid in the spring. The female crayfish carries eggs under her body for several weeks until they hatch. The eggs look like a ball of raspberries under the female's tail. The young crayfish look like tiny adult crayfish. After they hatch they hang on to the the female for a few days, then they crawl away to live by themselves. They eat the same kinds of food as the adults. Crayfish usually live about 2 years.