A quick guide to identifying crayfish

Initially, crayfish tend to all look like little brown lobsters. But once you learn what to look for, ID seems not just vaguely possibly, but actually easy and, dare I say, fun! So when trying to figure out what species of crayfish you have in your hand, you should take note of the following features: (A) coloration, (B) areola width, (C) rostrum shape, (D) chelae (claw) length, (E) carapace length, and (F) dactyl (thumb) shape. For more details on the anatomy of crayfish, visit the anatomy page.

What features to look for on a crayfish: A: coloration, B: Areola width, C: Rostrum shape, D: Claw length, E: Carapace length, F: Thumb shape

Key to the crayfish

1a. Rostrum margins without accessory spines → 2

2a. Chelae with two rows of tubercles on inner margin (Fig 2), rostrum margins straight, tapering………Big water crayfish, Cambarus robustus
2b. Rostral margins roughly parallel, acumen small……… Appalachian (eastern) crayfish, Cambarus bartonii
2c. Rostral margins convex, tapering; dactyls notched at base, body mottled, chelae obvoiusly so (Fig 3)………Calico crayfish, Faxonius immunis

 

1b. Rostrum margins with accessory spines (Fig 1) → 3

3a. Carapace covered in tubercles (Fig 4) and usually red, chelae long and narrow → 4

4a. Chelae more robust; areola nearly absent (Fig 6); with an enlarged tubercle near base of propodus (Fig 7); tubercles on back are larger than those of P. acutus and lighter than carapace………Red swamp crayfish, Procambarus clarkii
4b. Black wedge-shaped band on top of abdomen (Fig 8); chelae narrow, lacking space between dactyl and palm when claws closed; areola more open than P. clarkii; lacking tubercle at base of propodus, or palm ……… White river crayfish, Procambarus acutus

3b. Carapace smooth, chelae robust, male gonopods end in two straight elements (Fig 5) → 5

5a. Dactyl S-shaped (Fig 9) → 6

6a. Wide areola (Fig 6), carina between marginal spines on rostrum (Fig 10) ……… Northern clearwater crayfish, Faxonius propinquus
6b. Narrow to linear areola (Fig 6); red spot on each side of carapace (Fig 11) ……… Rusty crayfish, Faxonius rusticus
6c. Narrow to linear areola; chelae bluish (Fig 12) ……… Virile crayfish, Faxonius virilis

5b. Dactyl straight, or straight and hooked at tip → 7

7a. Dark band on abdomen (Fig 8) ……… Allegheny crayfish, Faxonius obscurus
7b. Sharp spines on its cheek (Fig 13) ……… Spiny-cheek crayfish, Faxonius limosus

Visual guide to the key

 

Fig 1: Rostrum margins with accessory spines

Fig 2: Chelae with two rows of tubercles on inner margin

Fig 3: Dactyls notched at base, chelae mottled

Fig 4: Carapace covered in tubercles

Fig 5: Gonopods end in two straight elements

Fig 6: Narrow vs wide areola

Fig 7: Enlarged tubercle near base of propodus

Fig 8: Black wedge-shaped band on top of abdomen

Fig 9: S-shaped dactyl

Fig 10: Carina in center of rostrum

Fig 11: Prominent red spot on side of carapace

Fig 12: Chelae blue to greenish

Fig 13: Sharp spines on cheeks

Other Keys to Crayfish

There are lots of other keys, some more, some less technical available online. Here are a few:

  • Crayfish of the White River (PDF)
  • Crayfish of New England (PDF)
  • Crayfish of Nebraska (PDF)
  • Crayfish of Pennsylvania (DOC)
  • Crayfish of Oklahoma (PDF)
  • Crayfish of Ohio (PDF)
  • Crayfish of Maryland (PDF)
  • Anatomy glossary (link)