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Coconut Crab’s Pinch Among the Strongest in the World

The unusual crustacean’s pincer rivals the bite of a lion

(Shin-ichoro Oka)
smithsonian.com

The coconut crab sounds like something on the menu at Red Lobster, but the large crustacean, Birgus latro, is something you don’t want anywhere near your mouth. That’s because pound for pound the crab has a crushing force few animals on the planet can rival, according to a recent study published in the journal PLOS One.

Japanese researcher Shin-ichiro Oka, at Okinawa Churashima Research Center, recently collected 29 of the crabs, which live on islands throughout the Indian and Pacific Oceans and can grow up to 18-inches long and weigh up to 9 pounds, reports Ben Guarino for The Washington Post. Using a stainless steel force-measuring stick, he calculated the crushing force of the crabs’ large claw. Oka estimates that based on body size, the largest-known coconut crab could crunch with roughly 742 pounds of force.

“The pinching force of the largest coconut crab is almost equal to the bite force of adult lions,” Oka tells Will Dunham at Reuters. “The force is remarkably strong. They can generate about 90 times their body weight.”

The pinch-force of the crab exceeds that of any other known crustacean, according to a press release. If a human had the same pinch strength to body-weight ratio as the coconut crab, Oka says, they would be able to produce six tons of crush force. Among terrestrial animals and when adjusted for body size, the crab's size to crush ratio is second only to the bite of the saltwater crocodile, which has a bite force that rivals T. Rex

So why does a crab need such a powerful tool? Well, Guarino explains that its name is apt. The crab does sometimes eat coconuts, which require a massive amount of force to bust open. Unlike other hermit crab species, the coconut crab has no shell to protect it, just a calcified outer skin, so the mega-claw also acts as a threatening defensive weapon.  

Oka is not sure exactly how the crab produces so much force and is leaving the physiology and biochemistry to other researchers. But he knows first hand the effects of the claw, getting nipped on the hand by crabs twice during the study. “When I was pinched, I couldn’t do anything until they unfastened their claws,” he tells Guarino. “Although it was a few minutes, I felt eternal hell.”

He’s lucky to escape with just a sore hand. The crabs have been known to chomp on chickens and even kittens.

About Jason Daley

Jason Daley is a Madison, Wisconsin-based writer specializing in natural history, science, travel, and the environment. His work has appeared in Discover, Popular Science, Outside, Men’s Journal, and other magazines.

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