The blue crab is a important bottom-dwelling predator and a member of the swimming crab family, Portunidae. It is widely distributed from Nova Scotia to northern Argentina, but along the coasts of North America, it is most abundant from Texas to Massachusetts. Blue crabs are opportunistic and will feed on a variety of live and dead fish, crabs, clams, snails, eelgrass, sea lettuce, and decayed vegetation. Male and female crabs can be distinguished by examining their segmented abdomen. The abdomen is folded and fitted snugly into a groove on the underside of the crab.
Crabs grow by molting or shedding their shell.
Just prior to molting, the crab is encased in both the hard, old outer shell and a soft, new one just beneath it. The formation of a new shell is evident along the margins of the swimming paddles of a crab. The earliest indication of the new skeleton is the formation of a black line along the rim of the paddles. Immediately after the molt, the crab's new shell is pliable and easily stretched. Large amounts of water are consumed prior to and shortly after the molt, causing the soft shell to expand and increase in size.