Crayfish Fast Facts
Crayfishes display a variety of colors that sometimes change over the lifespan of an individual. The color pattern of this juvenile signal crayfish allows it to blend in with the stream bottom.
Crawfish, crawdad, mudbug, yabby. These all are names for one charismatic critter: the crayfish. Crayfishes live in rivers, streams, swamps and lakes throughout North Carolina. Gently flip or roll a submerged rock or log, or shuffle through an underwater pile of leaves, and you will likely see a crayfish either pretending to be a shapely stone or propelling itself backward with its muscular tail. Our Museum Curator of Non-Molluscan Invertebrates, Dr. Bronwyn Williams, created the following list of fun facts about crayfish.
What is a crayfish?
Crayfishes are arthropods, a name which translates as “joint foot.” Like all arthropods (for example, insects, spiders and crabs), crayfishes have a segmented body, jointed legs, and an external skeleton called an exoskeleton. To grow, arthropods shed their exoskeleton in a process called molting.
Crayfishes are decapod (“10-footed”) crustaceans. They have five pairs of walking legs and five pairs of smaller appendages, called swimmerets, on the underside of the abdomen. The front-most pair of walking legs bear the claws. If they lose a claw or leg, a new one grows in its place!
Freshly molted signal crayfish. Crayfishes do not go through a larval stage but molt several times in their first year, and then more slowly throughout their life. They make themselves scarce for several days until the new exoskeleton hardens.
Crayfishes vs. lobsters
Crayfishes are often called “freshwater lobsters,” but how accurate is this? Well, they are both decapod crustaceans, as are crabs and shrimps. Crayfishes share a most recent common ancestor with the clawed lobsters. Because of this close relationship, crayfishes and lobsters look awfully similar. But, they differ in several ways, including habitat – crayfishes generally live in freshwater or estuarine (brackish) habitats, and lobsters live in marine ecosystems – and the number and structure of gill filaments, which these critters use to breathe.
An American lobster side-by-side (and to scale) with the bottlebrush crayfish. Can you tell the difference?
Where do crayfishes live?
Crayfishes are found in all four hemispheres of the globe, but of the more than 650 species and subspecies known, ¾ occur in North America, and of these, most are found in the southeastern United States. North Carolina alone has about 50 species of crayfish.
What do crayfishes eat?
Crayfishes are omnivores, and will eat almost anything, including vegetation, algae, worms, macroinvertebrates, fish eggs, small (usually injured) fish … even carcasses.
Crayfishes are host to many smaller organisms living in symbiosis. Some of these symbioses are opportunistic (i.e., “you look like a good place to hang out”), and some are obligate, which means the smaller critters need to live on the crayfishes at some point in their life cycle.
In North America, the two major groups of obligate symbionts that live on crayfishes are branchiobdellidans, or crayfish worms, and entocytherid ostracods, a type of seed shrimp. Both are grazers, feeding on algae and other organisms that build up on the surface of their host.
Branchiobdellidans, or crayfish worms, residing on a signal crayfish.
Crayfishes at the Museum
The Museum’s Non-Molluscan Invertebrate Lab is home to one of the largest crayfish collections in the world. The Lab is also home to nearly a dozen scientists, technicians, interns and volunteers who are all cray-zy about crayfish! The late Dr. John Cooper, former Director of Research and Collections and Curator of Crustaceans at the Museum, was a renowned crayfish taxonomist. He described many crayfish species, including two named after Museum staff. The current Curator of Non-Molluscan Invertebrates, Dr. Bronwyn Williams, is also a crayfish and crayfish symbiont taxonomist.
Dr. Bronwyn Williams holds a diminutive specimen with an outsized name — hillbilly hairy crayfish — a new species she formally described in April, 2018.