Illinois Natural History Survey - University of Illinois

Devil Crayfish

Susan Post

Mudbugs, ditch bugs, river lobsters, crawly bottoms, or crawdads are all common names for crayfish, a group of arthropods that resembles miniature lobsters.  Crayfish are common inhabitants of wetlands—from springs to large rivers, damp meadows to swamps and ditches. There are approximately 353 species of crayfish in the U.S. with 95% of them found in the Southeast. Illinois has 21 species of native crayfish.

A species found throughout Illinois  is the devil crayfish, Cambarus diogenes, named after the Greek philosopher Diogenes. They are multicolored, brown to brownish red, green to blue, and are 36 to 48 mm in length. Like all crayfish they have two body regions, a cephalothorax and abdomen. The cephalothorax is the head and thorax fused together and enclosed in a hard outer covering called a carapace. Crayfish breathe through gills that are located under the carapace. Their eyes are on moveable stalks that allow sight in different directions. Five pairs of jointed legs are present on the cephalothorax. The first pair are pincerlike and called chelae. On the last segment of the abdomen is a broad flipper that helps propel the crayfish through the water. By folding their abdomens down and forward, they are also able to swim backwards.

Crayfish are omnivores and will consume whatever food is available. While their primary food is usually decaying and living plant material, they will also consume aquatic worms, insects, snails, and dead animal matter.

The devil crayfish is abundant in the Shawnee Hills and the Coastal Plain of southern Illinois, while it is less common in northern and western Illinois. It is found primarily along streams or in lowland areas having clay soil. It is in these lowlands that colonies often occur with hundreds of chimneys.

The devil crayfish lives in a burrow with a cone-shaped mud chimney. Its burrow can be up to a meter in length and is usually at the side of a stream or pond. The chimney-topped hole leads to an underwater chamber and a second nearly horizontal tunnel leads into the stream. The crayfish does its digging at night. The chimneys are piles of pellets of mud or clay that the crayfish brings up and deposits around the opening of its burrow.  These burrows can serve as refuges not only for the crayfish but other organisms. An interesting relationship has developed with the endangered Hines emerald dragonfly and the devil crayfish. The dragonfly’s larvae will spend time in these burrows if their primary habitat dries up; however, the crayfish are potential predators of the dragonfly. This relationship is being studied at the Illinois Natural History Survey.

Crayfish leave their burrows either in the fall or late winter-early spring to mate in open water. The females will carry the sperm until oviposition. In Illinois, the devil crayfish will produce eggs from March to May. The female carries the eggs on the short appendages of her abdomen. These abdominal appendages are in constant motion to keep water flowing over the eggs. Females brood the eggs until they are hatched. The newly hatched crayfish hold onto their mother until they molt two or three times.  Once the young leave their mother, they seek cover in rocky parts of streams or the marginal vegetation of standing water until they are large enough (about 20 mm in length) to burrow. The young crayfish will become capable of reproducing after they have molted 6–10 times.

Threats to crayfish populations include habitat damage caused by impoundments, stream channelization, pollution, and sedimentation. The biggest threat,however, is non-native crayfish introduced as fishing bait.

 

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See also crayfish



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