A new study has found that the clumsy coconut crab is the one with the stronger grip than any other animal.
According to new research published in the journal PLOS ONE, this crustacean’s claws are, in fact, more difficult to close than most animals can bite – with the exception of crocodiles.
Shin-ichiro Oka, lead researcher in the zoology laboratory at Japan’s Churashima Research Center, and colleagues said that during the course of this study, data collection for analysis was carried out. This is a big challenge, because the large claws of this crab have clamped researchers many times.
However, Oka and his colleagues persisted, and they captured 29 coconut crabs in northern Okinawa to weigh and measure. Coconut crab (Birgus lastro) is the largest terrestrial crustacean. It is related to hermit crabs – they share a common ancestor more than 2 million years ago. However, unlike hermit crabs, the coconut crab does not need to borrow a shell for protection, its body is already calcified and hard on the outside.
Coconut crabs are found along islands in the Indian and Pacific Oceans. This animal can weigh up to about 4kg and can use its impressive claws to open coconuts.
Of all the animals, the ten-legged crustaceans, including crabs, lobsters and shrimps – can produce the greatest strength by body mass with their claws. However, no one has ever tested the strength of a large coconut crab.
These giant coconut crabs can even climb trees and other vertical surfaces with their powerful legs. And their massive claws can crush seeds, fruits and even the spongy cores of fallen trees to eat.
The researchers used a stainless steel sensor to test the grip strength of 29 captured crabs. The results show that the maximum clamping force is between 29.4N and 1765.2N.
For comparison, according to a study published in the journal Proceedings of the Royal Society B in 2010, a human bite can generate a force of up to 1,300N in molars.
Miracles of strength
Of course, humans are much bigger than coconut crabs. It is the body size that determines the strength of the claws of this crab. Oka and colleagues found that the larger the crab, the stronger the grip. If the largest coconut crab weighs about 4kg, the scientists calculate that it can exert a clamping force as strong as 3,300N – greater than any other crustacean.
The researchers concluded that, on the basis of body mass, this strength exceeds that of any animal, including crocodiles. Coconut crabs are solitary and very aggressive, they often make war with other coconut crabs and with potential predators and competitors. Because they are not limited by shell size like their hermit crab relatives, coconut crabs are free to develop exceptionally large bodies and claws.
