The blue crab is native to the western edge of the Atlantic Ocean from Nova Scotia to Argentina. It has been introduced (via ballast water) to Japanese and European waters and has been observed from the Baltic Sea, North Sea, Mediterranean Sea and Black Sea.

The natural predators of the blue crab include eels, drum, spot, trout, some sharks, and cownose sting rays. The blue crab is an omnivore, eating both plants and animals. Blue crabs typically consume thin-shelled bivalves, annelids, small fish, plants and nearly any other item they can find, including carrion and other blue crabs.

Male and female blue crabs can be distinguished by their "aprons", or their abdomens. Male crabs have a long, narrow apron while mature female crabs have a wide, rounded one. A common mnemonic is to remember that if the apron looks like the Washington Monument, the crab is male; if like the U.S. Capitol, it is female.

Chesapeake Bay Blue crabs undergo a seasonal migration; after mating, the female crab travels to the southern portion of the Chesapeake, fertilizing her eggs with sperm stored up from the last mating months or almost a year later. In November or December, the female crab releases her eggs. The crabs hatch in a larval form and float in the mouth of the bay for four to five weeks, then the juvenile crabs make their way back up into the bay.