Fiddler crabs (Uca pugnax)

Fiddler crabs are small (1 to 3.5 cm, or 0.5 to 1.5 inches) crabs that live in large groups on mud or sand near water. They also spend time in shallow burrows, which they dig in the mud. During low tide, the crabs are out on the mud flats. During high tide, the crabs crawl into their burrows. They take a small piece of mud and plug up the entrance to prevent water from coming in. Burrows also provide a safe retreat if a predator is nearby. Water birds, raccoons, and fish prey on fiddler crabs.

Fiddler crabs use their claws to gather food. They pick up small amounts of mud or sand and use their mouthparts to sift for detritus and algae in the sand. When they are done sifting, they spit out the leftover sand "pellets." There are often piles of sand pellets surrounding fiddler crab burrows. Male fiddler crabs, however, have one large claw (they may be right- or left- handed) and one small claw. Males do not use their large claws to capture or crush prey. They use them attract mates! Males wave their big claws at females to attract them to a burrow for mating. If another male gets too close to the mating burrow, the crabs will wrestle with their big claws, trying to push the other one away.