Consider elephant tusks, elk antlers, rhino horns or the curved canines of the extinct sabre-toothed cat… these weapons may be enormous, but, proportionally, it’s the male fiddler crab that owns the mightiest weapon on record.
The male’s larger claw can be half of its total body mass – the equivalent of carrying your entire bodyweight as one of your arms, everywhere you go. Never has the expression ‘red in tooth and claw’ seemed more apt. But it’s not so simple: these crabs are not violent.
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There are over 100 species of fiddler crab living in the tropics around the globe. Males defend burrows in the tidal zone from rivals, and passing females choose those they want to mate with, favouring the biggest claws and prime burrows.
The massive claws require so much energetic investment that only the fittest individuals brandish the most impressive examples. So for the females, brawn is best.
A male crab’s muscle-packed claw can pinch with a force four times stronger than that needed to puncture an opponent’s shell – with such a destructive weapon, you might expect to see beaches and mudflats strewn with carcasses from battles.
But that’s not the case. In fact, most species of fiddler crab rarely fight, but they wave their claws thousands of times a day, as a signal of strength to nearby crabs.
Opponents assess one another by the size of their adversary’s claw and the frequency with which they wave it.
Smaller clawed crabs invariably back down: the best-endowed crustacean nearly always wins without a fight.
“So here you’ve got animals with lethal weapons and yet they’re never using them to kill,” says Professor Doug Emlen, a biologist at the University of Montana and author of Animal Weapons: The Evolution of Battle.
“It leads to this paradox that the species with the biggest weapons of all are often the most peaceful.”
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