Male fiddler crabs regrow weaker claws and bluff their rivals anyway
A male fiddler crab carries one claw far bigger than the other, and he uses it to fight, to shed heat and to beckon females in waves timed with his neighbours. If he loses it, the replacement often looks just as big but is much weaker, and other crabs usually fall for the bluff.
Around a hundred species live on mudflats, beaches, lagoons and salt marshes from West Africa and the western Atlantic to the Indo-Pacific and Portugal's Algarve. None are large: the biggest of their family, Afruca tangeri, measures just over 5 cm across. They eat by scooping sediment to their mouths, sifting out algae, microbes, fungi and detritus, and leaving the cleaned grains as little sand balls beside the burrow.
Courtship is a performance. A male raises the oversized claw and draws it back toward himself in a come-here gesture, waving slowly when no female is in sight to save energy and speeding up once he spots one. Neighbouring males often wave in unison, but a female tends to pick whoever leads the rhythm, so the synchrony probably emerged by accident from males racing to be first. Males also drum at their burrow entrances, and some species build chimneys, hoods, pillars or other mud structures around the opening, which make a burrow more attractive to females.
Females weigh claw size, wave quality and property. They favour males holding territory with a burrow, preferably a wide one, where mating happens and eggs are incubated. A female carries her egg mass underneath for about two weeks in the burrow before releasing the eggs on a receding tide, and the larvae drift as plankton for another fortnight.
Fights over mates and burrows can tear off a major claw. It grows back at the next moult, on the same side, often similar in size yet substantially weaker, a case of dishonest signalling documented in Austruca mjoebergi. The big claw also works as a radiator, drawing heat out of the body, and it cools faster while waving. Life is short: two years at most in the wild, three in captivity. In laboratory conditions the crabs keep a tidal rhythm, darkening by day and paling at night.
Source: Fiddler crab
