Fiddler crabs come from the family Ocypodidae, and blue crabs from the family Portunidae.
Most fiddler crabs live on the shoreline in temperate and tropical waters.
Fiddlers also are found in mangrove swamps and mud flats. The male fiddler crab has one claw much larger than the other. It is used to attract females and defend territory. Fiddler crabs can't swim. Blue crabs, also known as the Chesapeake Bay crab, live in the Atlantic ocean.