Any of about 65 species of decapod s (genus Uca ) whose males hold one claw, always much larger than the other, somewhat like a violin.
Both claws of the female are relatively small. Fiddler crabs often live in large numbers on beaches in temperate to tropical regions of the world. They inhabit water-covered burrows up to about 1 ft (30 cm) deep and feed on algae and other organic matter. Common North American species (e.g., marsh fiddler, china-back fiddler) live all along the U.S. Atlantic coast. Brightly coloured, they range in body size from about 1 to 1.2 in. (2.5 to 3 cm).