Washington has just one native crayfish (Pacifasticus leniusculus)with a uniform brown coloration, white or light coloration at the claw joint, and a smooth surface on the claws and carapace (head and back) compared to the nonnatives. The nonnatives have pronounced bumps on their claws.

Signal Crayfish are a decapod crustacean, related to lobsters, shrimps and crabs.  P. leniusculus is large as crayfish go, reaching the minimum legal size of 3 ¼ inches in about three years, but often growing to 6 inches or more in 5 or 6 years.  Crayfish prefer fresh animal food if they can get it, but they also eat a variety of aquatic plants.  People think of them as scavengers because they are not very good at chasing down live prey.  In fact, crayfish seem to prefer fresh food to decaying matter.  Their diet may change considerably as they pass from the juvenile to the adult stage.  This may help explain why juveniles rarely enter traps.  Crayfish themselves serve as meals not only to humans but to a number of birds, fish and mammals as well.

P. leniusculus mates in the fall, and the females extrude from 100 to 300 eggs shortly thereafter.  The eggs or “berries” remain attached to the underside of the female through the winter and hatch in late spring.  The young crayfish remain as passengers on the mother for several weeks, molting twice before finally venturing out permanently on their own.  In summer, a typical crayfish lake will contain immature males and females from the previous year which have not yet mated, adult males, adult females which have recently shed their young, and many newly-hatched juveniles.  A few of the earliest born juveniles may grow enough to mate the same fall, but the majority are not able to reproduce until the following fall, when they are 17 or 18 months old.  At this age, they are generally still below the minimum legal size.  Females may spawn twice or more in a lifetime.

Our species normally requires at least three years to grow to the minimum 3 ¼ inch legal size for harvest, by which time most have had a chance to reproduce.

Different age groups prefer different habitat—the juveniles favoring shallow, weedy areas where they can find protection from predators (and each other, since they are cannibalistic), and the large adults favoring deeper areas, perhaps to avoid birds and land mammals.