Even animals need to be alert when they sleep. A giant coconut crab devoured a sleeping seabird, a video shows.

In the video, a giant crab from the Indian Ocean can be seen attacking and eating an adult red-footed seabird sleeping on a low-lying branch.

Giant Coconut Crabs

Growing to more than 3 feet, coconut crabs or Birgus latro are the world's largest land dwelling arthropods. Named after their strength of opening coconuts, these crabs have armor-clad legs and giant claws that can carry as much as 61 to 66 pounds of weight despite weighing only about 8 to 9 pounds when fully grown.

These crabs, instead of snapping their claws, apply a crushing pinch force. A previous study showed that the terrestrial crabs have a pinch force of 750 pounds. For reference, humans have a moderate bite power of 265 pounds. The crab's pinch force is comparable to that of a lion's bite force.

The mighty claws of these arthropods are a result of evolution. The stripping of their shells led them to develop a calcified abdomen as they grew larger. Their claws are quite strong, enabling them to climb trees similar to the spider-like crab species found to live in trees.

Giant coconut crabs are omnivores. They eat fleshy fruits but can also devour meat when it is available, as is in this case.

Altering The Ecology Of Islands

The video, recorded about a year ago by Mark Laidre, a biologist from Dartmouth College, showed the preying behavior of giant coconut crabs while observing the crustacean in the Chagos Archipelago. The crab snatched the unsuspecting bird, snapped its wings and clawed through its body. About 20 minutes into the video, five more coconut crabs swarmed the bird.

Laidre's observations, which he wrote in a paper published in the Frontiers in Ecology and the Environment in Nov. 1, led him to conclude that parts of islands inhabited by more coconut crabs have fewer nesting birds. He noted that coconut crabs cannot move freely so there are areas in the island where they are aplenty.

"They're not belligerent. They're curious," shared Laidre in an interview. "They're not coming and jumping and trying to attack you. Coconut crabs more should fear humans."

In 2014, residents of Hawaii's Salt Lake neighborhood caught a giant coconut crab. Coconut crabs are not native to Hawaii. In fact, possession of this crustacean is a Class C Felony and constitutes a three-year imprisonment and a fine of $200,000.

Watch the video below:

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