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Perhaps you've caught a "crawfish" or two from a stream, river, or other water body to use as bait. Or perhaps you've dined on some yourself. You may have even seen them in aquarium shops. Did you ever wonder how many types of crayfish there are or what life might be like for one? Freshwater crayfish are aquatic crustaceans that closely resemble their marine relatives, lobsters. Both have a jointed exoskeleton that shields their soft bodies, and five pairs of legs, including a pair of large claws called chelae. However, unlike their marine equivalents, adult crayfish are much smaller, reaching a maximum total length of about 4 ½ inches.
Crayfish
live in many types of aquatic habitats, including streams, rivers, lakes,
ponds and swamps.
They also
reside in habitats that are less well known. On North Carolina's Coastal
Plain, water from the swamps overflows into the roadside ditches often
creating a yearlong pool of standing water. For some crayfish, these
stagnant pools provide a home to feed, grow and reproduce. Some species
dig burrows downward to the water table in swamps and wet pastures,
or even in your back yard. These burrows may develop into an intricate
maze of tunnels and chambers. Often at the surface, however, the only
telltale signs of subterranean architecture are many holes on the surface,
sometimes with "chimneys" of mud-balls excavated as the burrow
develops.
The crayfishes that occur in North Carolina live for 2-3 years, on average. To grow, crayfish must shed their exoskeleton several times, a process known as molting. Just after molting, they are soft and vulnerable to predators. Crayfishes breed more than once during their lives. Males are usually reproductively active for only part of the year (the season varies among different species). After mating, females carry their eggs attached to their abdomen (termed "in berry"). They even carry the young in this manner until they are large enough to survive on their own. Crayfish play an important role in the function of aquatic ecosystems. Crayfish are omnivores. They usually consume live aquatic plants; however, they also eat insects, snails, small fish, periphyton and other aquatic organisms. Crayfish are also considered scavengers, since they regularly consume dead animal and plant material. They forage mostly at night and seek shelter from predators during daylight. Crayfish serve as a food source for many animals, such as game fishes, otter and other mammals, birds and reptiles. Fish consume as much as two-thirds of the annual crayfish production. Crayfish serve as a major link in an intricate aquatic food web by consuming such a variety of foods and by making processed nutrients available to other animals. In this way, they facilitate the cycling of nutrients and energy in the entire aquatic system.
In addition to their ecological importance, crayfish are also valued economically. Larger "crawdads," such as the red swamp crayfish (an introduced species established in North Carolina), are considered a delicacy of Cajun cooking. Each year in the United States, 65 to 85 thousand metric tons of crayfish are harvested commercially from both wild and cultured populations. This industry is centered primarily in Louisiana and Texas. Crayfish are also frequently used as bait. Unfortunately, this practice has led to some accidental introductions of non-native crayfish into new areas. Among other things, exotic crayfish negatively impact invaded ecosystems by competing with native species and destroying aquatic plants that provide food and shelter for native animals. PLEASE DO NOT release crayfishes into North Carolina waterways! Once a non-native species is established it is impossible to eradicate without harming native animals.
Despite the important ecological and economic role of crayfish, there is still much to learn about their distribution and taxonomy. In the United States and Canada, there are currently 350 recognized taxa of crayfish. The greatest diversity of these crayfish occurs in the Southeast. In North Carolina, there are at least 40 species, some of which are native only to this state. While the intensive work of biologists has expanded the known ranges of different species and led to the discovery of possible new species, there are many mysteries remaining. Therefore, it is difficult to pinpoint declining or threatened populations. There is little question that habitat degradation, including the dredging and damming of waterways, poses a threat to some crayfish populations. These and other human impacts can result in decreased habitat and food available to crayfish. Declines in water quality can also harm crayfish populations, either directly or by negatively affecting their prey or predators.
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Crayfish
can be identified by several physical characteristics. Because many
species of crayfish look similar, it is difficult to tell them apart
without a microscope and intensive study. Taxonomists use the traits
least likely to vary according to environmental pressures (e.g., temperature,
flow conditions). The most definite way to identify a crayfish to species
is by examining the sexual appendages (gonopods, or the first set of
swimmerets on the abdomen) of the reproductively active male. Unfortunately,
this character isn't always easy to observe, especially in the field.
Other characteristics commonly used include the shape and size of various
parts of the body, texture of the exoskeleton (i.e., whether it is smooth
or has spines, bumps, or small hairs), and body coloration and patterns
(e.g., solid, lines, mottling). Crayfish come in all colors, including
red, orange, yellow, green, tan, brown and even blue. Coloration can
vary widely among crayfish of the same species and isn't usually very
reliable. However, it can be a good place to start. See the 
Wildlife
is a gift often taken for granted.