What the male fiddler crabs lack in body size, he more than makes up for in claws. The large claw, or cheliped--which looks like a fiddle when moved in conjunction with the smaller claw--is used for communication, courtship, and combat. The smaller claw is used for eating and building a burrow.
When approached by a potential mate, the male fiddler crab begins to wave its large claw up and down. The higher he can raise it, the better his chances are of mating: larger claws require more effort to lift, so it's a good indication of the male's fitness. If he loses the large claw through injury or fighting, the smaller one will grow large to replace it. A new, smaller claw will also regenerate in place of the missing one.