Atlantic blue crab

The blue crab is a swimming crab of the western Atlantic Ocean and the Gulf of Mexico, and it has also been introduced to other parts of the world. It is an important food and fishery in the United States, especially in Louisiana, the Carolinas and Chesapeake Bay. It is Maryland's state crustacean.

Its scientific name, Callinectes sapidus, means beautiful, savory swimmer. The shell can reach about 23 centimetres across. It belongs to the swimming-crab family Portunidae, and unlike most crabs it can cross open water. It is a popular seafood, and also feeds many other animals. It sheds its shell many times as it grows.

Boys and girls

Male and female blue crabs are easy to tell apart. The flap on the belly, called the apron, is long and slender in males but wide and rounded in mature females. The claws also differ in colour: males have blue claws, and females' claws have red tips. The last pair of legs is flattened into paddles, so it is a strong swimmer. Males are often called Jimmies and females Sooks, in places like Chesapeake Bay.

A changing coast

A blue crab sheds its shell many times as it grows and is soft and vulnerable right afterwards. Females need eelgrass for their final moult, so rising seas may hurt them, while warmer water may give crabs better breeding conditions and a wider range. Warmer waters might help the species spread, but nobody knows yet how a larger crab population will affect the other animals around it.

On the globe

The model shows a blue-clawed swimming crab. Look for it along the coasts of the Atlantic and Gulf of Mexico.