Crayfish, or Crawfish, colloquially called crawdad, a freshwater crustacean related to the lobster. (The saltwater spiny lobster is also commonly called crawfish.) It is about six inches (15 cm) long and may be white, red, brown, orange, dark green, or black. The crayfish has two pairs of antennae, one long, the other short. Its cephalotkorax (fused head and thorax) is covered with a rigid shell, or carapace. A pair of large, pincerlike claws and four pairs of walking legs extend from the cephalothorax. The abdomen is made up of six ringlike segments. Four of these segments have short appendages used in swimming.

The crayfishThe crayfish has two pairs of antennae, a rigid shell, pincerlike claws, and four pairs of legs.
What Are the Differences Between a Lobster and a Crayfish?

Clawed lobsters and crayfish are very similar. They have the same body structure: the same number of legs, the same number of antennae, a long tail, two claws, and a hard outer shell. Both also have two compound eyes. In fact, crayfish look more like clawed lobsters than do spiny lobsters.

There are, however, two important differences between clawed lobsters and crayfish. The first is size. Adult crayfish are usually 2 to 6 inches (5 to 15 centimeters) long. Commercially sold American lobsters are usually about 8 inches (20 centimeters) long and can grow much longer if left unharvested in the sea.

The second major difference is where crayfish live. Lobsters live in the ocean. Crayfish inhabit lakes, streams, and rivers. Crayfish are common in North America, Asia, Australia, and Europe.

Crayfish live under rocks and debris on the muddy bottom of freshwater lakes and streams. They are active at night and crawl along the mud feeding on aquatic vegetation, worms, insects, mollusks, and decayed organic matter. Their pincerlike claws are used to crush and tear food into smaller pieces. When alarmed, the crayfish rears up, raising its claws threateningly. The fanshaped tail then propels the crayfish backward, flinging mud at the enemy.

When water is low and the crayfish's mudflat is exposed, it digs a burrow down to the water level; it constantly deepens the burrow as the waters recede, heaping up a ring of marble-shaped pellets of mud about the entrance. Raccoons and other predators catch crayfish by churning the mud around their burrows, causing the crayfish to come out to investigate.

Young crayfish are hatched from eggs and resemble adults except in size. They take several years to reach full size. Whenever the shell becomes too small, which occurs several times the first year, the young crayfish sheds it and grows a new one.

Crayfish are found throughout the world. There are about 500 species; 350 are found in North America. Crayfish are a popular food in the southern United States. They are caught with wood or steel traps.

Crayfish make up the families Astacidae and Parastacidae. North American species include Cambarus virilis, C. setosus, and C. bartoni. A typical European crayfish is Astacus fluviatilis.