Coconut crab pinches with force of a tiger bite

In a clenching battle between a tiger’s jaws and a crab’s pincers, who would win? The answer, it seems, depends on the crab.

The coconut crab – a resident of the Indian Ocean’s islands and the world’s largest land-dwelling crustacean – has the most forceful pinch of all crabs, with more brute strength than the jaws of most terrestrial animals, a new study has revealed.

A team led by Shin-ichiro Oka from Okinawa Churashima Foundation in Japan tested the pinching force of 29 coconut crabs (Birgus latro) on Okinawa Island.

These enormous crabs can weigh up to four kilograms – around the same as a small cat – and lift up to 30 kilograms. The multi-skilled crustaceans use their huge pincers to attack, defend and to open coconuts – a food source off limits to most animals.

Oka and his crew found a coconut crab’s pinching ability correlates with its body mass, with the largest mustering a pinching force of 3,300 newtons.

For comparison, a tiger bite has a force of around 2,200 newtons. Our puny jaws? Just 900 newtons.

“This force greatly exceeds that in all other crustacean species that have been reported, as well as the bite force for the majority of modern terrestrial predators, other than alligators,” the researchers write in the journal PLOS One.

They suggest that evolutionary changes in the shape of the pincers, and the length of muscle fibres, might be behind their extreme force. The trait allows coconut crabs to hunt other large animals with a hard shell, which in turn helps keep them big and strong. 

But the researchers say the testing process wasn’t all roses: “During our field study, obtaining data for analysis was challenging, as the large claws of this crab pinched us on multiple occasions.”