Los Angeles Times
The coconut crab’s pinch packs a punch
The land-dwelling giant’s claws can lift about 66 pounds and crush with about 750 pounds of force.
Coconut crabs might be the heavyweight champions of all crustaceans.
The largest landdwelling crab on Earth, Birgus latro, can lift about 66 pounds with its pincers and can pinch with about 750 pounds of force. That makes the coconut crab among the strongest terrestrial animals — only alligators and a few other species’ bites are more powerful.
These intimidating findings come from a new study published in the journal PLOS One, in which researchers at Okinawa Churashima Foundation in Japan measured the pinching prowess of 29 coconut crabs on Okinawa Island.
The crabs varied significantly in weight, ranging from less than a pound to about 5 pounds. Their pinches exerted about 7 to 400 pounds of force (or 29 to 1,765 Newtons).
During the challenging process of measuring and weighing the crabs, the researchers got pinched multiple times by the animals’ claws.
Since the strength of the crabs’ claws was strongly correlated with body mass, the study authors were able to calculate the pinching force of the largest recorded coconut crab. This 9-pound crustacean would have been able to pinch with about 750 pounds of force (or 3,300 Newtons).
To put that in perspective, a human’s bite (from the molar) exerts an average of 265 pounds of force. And an Olympic boxer’s average punch exerts around 770 pounds of force, although this is more of a push than a clamping force.
Coconut crabs, or robber crabs, may have gained their tremendous claws as they lost the need to carry a shell during the course of their evolution. These crustaceans are descended from a hermit crab ancestor that, up to about 5 million years ago, would have scavenged a hard snail shell to carry on its back for protection.
Without their shells, the crabs were able to grow larger and protect themselves by developing a hard, calcified abdomen, the study suggests. (Young coconut crabs do carry a shell, but only while they’re very small).
Using their super-crustacean strength, coconut crabs brandish their claws to ward off competitors and fight other animals for food and resources. But their claws aren’t just weapons, the authors wrote.
The crabs are found on islands across the Pacific and Indian oceans, and their powerful pincers give them access to all kinds of foods their competitors can’t get. Their menu options include other hardbodied animals, carrion, fruit and the fallen insides of trees.
Most important, though, they use their large claws to tear through the husks of their favorite foods: coconuts.