rusty crayfish factsheet

by Jeffrey Gunderson

Identifying crayfish can be very difficult. Positive identification requires looking at a number of characteristics and having enough experience to interpret them. Here are some general, easily-observed characteristics that can be used to help you identify mature adults of four common crayfish species found in the Great Lakes region. (Other species found in the region include Cambarus diogenes, Procambarus acutus acutus, and in southern parts of the region Procambarus clarki). The following are general identification guidelines and should not be used when positive identification is needed. Contact your local fishery management agency or Minnesota Sea Grant if positive identification is required.

4A: Composite drawing of O. rusticus and O. propinquus. dark spot on carapace of O. rusticus. 4B: dark patch and appearance of light colored stripeon abdomen of O. propinquus.

Rusty crayfish can generally be identified by their more robust claws, which are larger than either O. immunis' or O. virilis', and by the dark, rusty spots on each side of their carapace. The spots are located on the carapace as though you picked up the crayfish with paint on your forefinger and thumb (Figure 4A). The spots may not always be present or well developed on rusty crayfish from some waters.

O. propinquus has a claw very similar to the rusty crayfish, but lacks the dark spots on each side of the carapace. Instead, O. propinquus has a dark brown to black patch on the top of the abdomen ("tail section"). This gives the impression that a light-colored stripe runs along each side of the abdomen (Figure 4B).

Compared to the rusty crayfish, O. virilis can often be distinguished by its claws, which are more blue and have distinct white, wart-like bumps. The rusty claw, by comparison, is grayish-green to reddish-brown and is smoother (Figure 5).
Claw shape can help distinguish between the various species.

5A: O. rusticus-O. propinquus
Black bands at claw tips. Oval gap when closed. Smooth, S-shaped, moveable claw.

5B: O. virilis
No black bands. Gap is a mere slit when claw is closed. White wart-like bumps on claw.

5C: O. immunis
No black bands. Gap is a definite notch. Claws are narrower and elongate.

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 Page Coordinator - Debbie Bowen modified September 28, 2001