Despite their name, blue crabs typically have grayish blue or olive-green shells, with bright blue only on their claws and legs. The claws of mature males typically have purple-blue tips and the pincers of mature females are bright red.
There’s another easy way to distinguish a male from a female blue crab: Maryland locals know to turn the crab over and look at shape of its "apron” folded tight to its abdomen. Males have an inverted T-shaped apron, while females have a triangular apron that becomes rounder and dome-shaped as they mature. Adult females hold a bright orange, sponge-like mass of developing eggs under their apron for protection until they hatch.
As crabs grow, they shed their shells through a process called molting. The crab takes in water to expand which separates its upper shell from its lower shell. This is a vulnerable time for the blue crab as it slowly wiggles free from its old hard shell. The new, much larger soft shell slowly hardens, becoming a “paper shell” within 12 hours and fully hardened in two to three days. Male crabs continue to grow and throughout their lives and can molt from 21 to 23 times. Females molt 21 to 22 times and stop growing after a final molt when, in their soft-shelled state, they mate with a hard-shelled male.
Crabbing is part of Maryland's heritage, and blue crabs play an important role in the economy, culture and ecosystem of the Chesapeake Bay region.
A blue crab uses its large, powerful claws for ambushing small fish; cracking open mussels, snails and clams; gathering food and defending itself. Crabs walk sideways using three pairs of walking legs and have one pair of paddle-like legs they use to swim just below the water’s surface, migrating up and down the Bay and escaping from predators.
Learn more about blue crabs! Did you know that blue crabs’ scientific name, Callinectes sapidus, is derived from Greek and Latin and means “savory and beautiful swimmer?” An adult male blue crab is called a “jimmy,” an adult female is called a “sook” and an immature female is called a “sally.”
Blue crabs live along the Atlantic coast, from as far north as Nova Scotia to northern Argentina.
Adult blue crabs are bottom-dwelling predators and scavengers. They feed on snails, bivalves, crustaceans, fish, marine worms, detritus and nearly anything else they can find, including dead fish and plants, and occasionally juvenile blue crabs.
Males typically grow larger than females, sometimes reaching 9 inches from point to point on the shell. The minimum legal size for harvesting can change from year to year and from month to month during the harvest season. An annual Bay-wide winter blue crab survey is conducted by the Maryland Department of Natural Resources and the Virginia Institute of Marine Sciences. Hibernating crabs are dredged up from the bottom mud at numerous locations. Adult male, adult female and juvenile crabs are counted, and this data determines how many and what size crabs can be sustainably harvested from Maryland waters that year.
Loss of habitat and dead zones of low water oxygen levels, combined with the blue crab’s popularity as food for humans, has led to serious population declines. The number of Chesapeake Bay blue crabs has been slowly rebounding, thanks to harvest management, water quality improvements and restoration of underwater grasses, which juvenile and molting blue crabs rely on for shelter and protection.
Bony fish, sharks, rays, and large birds feed on blue crabs, and they are the preferred food of the endangered Kemp’s ridley sea turtle.
As the National Aquarium's general curator, Jack Cover ensures that all animals in our care thrive in healthy, beautiful habitats.