The blue crab takes its name from the brilliant blue of its claws and legs; the shell on top is olive green. Adult females can be told apart by the red tips on their claws, as if they had painted their nails. The shell grows up to 9 inches (23 cm) from point to point and a big crab weighs 1-2 lbs (0.5-1 kg).
Blue crabs belong to the swimming crab family. The last pair of legs is flattened into paddles, which they spin like propellers to swim sideways and even backwards at surprising speed.
Its scientific name, Callinectes sapidus, means "beautiful savoury swimmer". A soft-shell crab is simply a blue crab caught just after molting, before its new shell has hardened.
Blue crabs live along the western Atlantic coast from Nova Scotia to Argentina, including the whole Gulf of Mexico. They are most famous in the Chesapeake Bay, where they are the signature catch.
They favour estuaries, bays and salt marshes, where fresh and salt water mix, and move between shallow grass beds in summer and deeper channels in winter. Blue crabs have also spread to the Mediterranean Sea, where they are an invasive species.
Blue crabs eat almost anything: clams, oysters, mussels, small fish, worms, dead animals, plants and other blue crabs. They crack shells with their strong claws and use their smaller mouthparts to pick out the meat.
They are an important food for fish, birds, sea turtles and people.
Blue crabs are quick, aggressive and quick to raise their claws when threatened. In cold weather they bury themselves in mud and wait out the winter.
A female mates only once, just after her final molt, and the male guards her until her shell hardens. She can carry up to two million eggs in an orange mass called a sponge, then releases the larvae near the mouth of the bay. Most blue crabs live for about three years.
Callinectes sapidus is one of about 16 species in its genus and belongs to the swimming crab family Portunidae. It has not been assessed by the IUCN, but it is closely monitored because of its value to fisheries, especially in the Chesapeake Bay and the Gulf of Mexico.
Threats include the loss of seagrass beds where young crabs hide, low-oxygen dead zones in bays, and heavy fishing. Where it has been introduced, such as the Mediterranean, it can crowd out native species and damage fishing nets.
