Coconut crab

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These crabs pinch harder than most animals bite

The world’s largest land-living crustaceans, coconut crabs (Birgus latro, pictured), can grow up to a meter long, but their real claim to fame is their strength: They’ve been known to lift more than 30 kilograms and earn their names by cracking into coconuts to eat. Exactly how strong a pinch from a coconut crab’s claw is, though, was a mystery—until now. Researchers captured 29 coconut crabs on Okinawa Island in Japan and had them clamp down on steel force sensors. Pinching forces ranged from 29.4 to 1765.2 newtons among the collected crabs. (For reference, the human bite is about 340 newtons at most.) Because the crabs’ pinching forces were significantly correlated to their body weights, the researchers calculated that a 4-kilogram coconut crab should be able to exert a shocking force of 3300 newtons with its claw. That’s greater than the bite of almost any animal on land, including leopards, most bears, and wild dogs. As the researchers write today in PLOS ONE, the coconut crab’s powerful claw is added evidence that they diverged from humble hermit crabs some 4 million years ago. Such a formidable weapon would help the crustaceans shed the need for a protective shell, fend off predators, and access new food sources, like coconuts, with ease.

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