Fiddler crabs are a group of ocypodid crabs that make up the genus Uca. Like many other animals they rely on ‘signaling’ to attract mates. The over-sized chela (claw) that males sport, though fearsome, is used primarily as a signal to attract females. During courtship males will wave their claws in the air and tap them on the ground in an attempt to convince females that their claw is the biggest and strongest. Fights will often break out between males, with the males with larger claws generally winning and getting the better females. These fights are thought to be a means of impressing females and asserting dominance.
Some fiddlers (like U. l. mjobergi) have been shown to bluff about their abilities. Occasionally when regrowing a lost claw the fiddler will instead grow a weak claw, thought large it would be useless in combat. The crab will still brandish this claw and intimidate crabs with smaller and stronger claws. However, its still unknown if the crab is consciously bluffing or not.