Blue crabs have a hard upper shell, typically brownish green in color, that narrows into a sharp spine on each side, and a white abdomen. The shell is about 2.5 times as wide as it is long. Blue crabs have two large claws, three pairs of thin walking legs, and one pair of paddle-like swimming legs. You can distinguish mature males from females by their claw color and apron (abdomen) shape. Females' claws are blue on the inner and outer surfaces with bright red tips. The male’s apron is shaped like a narrow, inverted T, and females have a broader, rounded abdomen. Blue crabs can grow to over 8 inches wide (including the spines) and typically weight 1 to 2 pounds.
Range and Habitat
Range from the northern Atlantic coast through the Gulf of Mexico down through most South America's eastern coast. Bottom dwellers, adult blue crabs are found in practically every bottom type from mud flats in the shallow waters of the Gulf to grass beds in almost fresh estuarine waters. They often hide in structure such as marsh and sea grass or oyster reefs, or bury in soft mud bottoms for protection from predators. Females are typically found in the higher salinity waters of coastal lakes and bays, while males can tolerate extremely low salinities and can be found in many tidally-influenced freshwater bodies.
Typically mature after 12 months and can mate and spawn almost year round, with peak activity in spring and summer. Mate in brackish waters of the upper estuary just after the female molts, while her shell is still soft. After mating, the male stays to protect the female until her new shell hardens. The female stores the sperm in receptacles for several months. Females move to saltier coastal Gulf and estuarine waters to spawn. As the fertilized eggs develop, the female moves them to their underside and carries them until they are fully developed. At this stage, the female is known as a “sponge” or “berry” crab. A female can carry up to 3.5 million fertilized eggs. Eggs hatch in about two weeks. Tides transport newly hatched larvae from estuaries to adjacent continental shelf waters where they molt several times. Crabs grow by molting--their hard shell restricts growth, so they must shed it to increase in size. Assisted by winds and tides, post-larval blue crabs migrate back into shallower, less saline waters in middle and upper estuaries where they grow and mature. Live 3 to 4 years.
Blue crabs are opportunistic feeders, eating whatever food is available. Larval blue crab feed on plankton, but as they grow and settle to the bottom, their diet expands. Juveniles and adults feed on small fish, bivalves, crustaceans, plant material, detritus, and other blue crabs. Shrimp, jellyfish, fish, and other plankton-eaters feed on larval blue crab; a number of commercial and sport fish, turtles, birds, and alligators prey on juvenile and adult blue crabs.