Coconut crab’s pinching force is equal to bite force of adult lion: research

Coconut crab’s pinching force is equal to bite force of adult lion: research

The pinching force of an adult coconut crab is almost equal to the deadly bite force of an adult lion, according to a study published in the journal PLOS ONE.

The so-called coconut crabs (Birgus latro), which inhabit islands in the Indian and southern Pacific oceans can grow up to 9 pounds in weight, with a leg-span of 3 feet. These large crabs can easily crack open the hard shells of coconuts.

A group of Japanese scientists measured these crabs’ pinching strength with the help of sensors, and were surprised to find that an adult coconut crab’s claws can exert pinching force of up to 3,300 newtons or 742 pounds of force, nearly 4.5 times greater than the grip strength of an adult man.

Lead researcher Shin-ichiro Oka, a marine biologist at Japan’s Okinawa Churashima Foundation, said, “The pinching force of the largest coconut crab is almost equal to the bite force of adult lions. The force is remarkably strong. They can generate about 90 times their body weigh.”

Oka added that the coconut crabs use their powerful claws for self-defense as well as for accessing hard food sources. They are also capable of lifting up to around 66 pounds (30 kg).

The scary island-dwelling species can be found on islands spread from Zanzibar in the west to Gambier in the east, with Christmas Island having a particularly thick population of the scary creature.

The researchers found that the pinching force of the coconut crab was extremely strong and increased with the size of the crab. According to a previous study, the largest coconut crab known weighed 4 kg (8.8 pounds). Based on the data from this new experiment, a crab that large would have a pinching force of 3300 Newtons. This force greatly exceeds both the pinching force of other crab species and the bite force of most land predators, with the exception of alligators.

“I was pinched two times,” says Oka. “When I was pinched, I couldn’t do anything until it unfastened its claw. Although it was only a few minutes, I felt eternal hell.”

Coconut crabs (Birgus latro) are the largest terrestrial crustaceans and are remarkably strong, able to lift nearly 30 kg (66 pounds). They use their prodigious claws to capture and manipulate food items with hard exteriors (including coconuts), as well as to fight other crabs and defend themselves.

The closer muscle fiber sarcomere length was measured in the larger left claw of a voucher coconut crab specimen (OCF-Cr00051 deposited in the Okinawa Churashima Foundation, 51.3 mm ThL, male, preserved 70% ethanol solution after 10% formalin fixation). The muscle tissues (dorsal-ventral, mid-way along the manus) were embedded in paraffin, sectioned to 7 μm, and stained with phosphotungstic acid hematoxylin (PTAH) for histological observation. Single sarcomere lengths from a fiber on the slide were measured using a digital microscope (OLYMPUS, BX53). Muscle stress in this specimen was calculated using the following formula: S = F/Asin2θ, which was obtained in a previous study [10], where F is the force applied to the base of the dactyl, estimated from the relationship between the actual pinching force and body weight (Fig 2), and the mechanical advantage (Lber/L1, Fig 1C). The value of A (the area of one side of the closer apodeme) and θ (the mean angle of the fiber attached the closer apodeme) of the claw specimen were directly measured.

Among the force associated with the closure of crustacean chelae and vertebrate jaws few exceed the upper range of these values, while the pinching forces of Cancer spp. and the coconut crab do exceed the upper limit.

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