Nov 6, 2017

Coconut crabs also eat birds

A coconut crab kills a red-footed booby. Photo: Mark Laidre / Dartmouth

For decades, scientists believed the nine-pound coconut crab ate, well, coconuts. But in March 2016, biologist Mark Laidre watched one catch, kill and devour a red-footed booby. He described the encounter in a paper published in Frontiers in Ecology last week.

Why it matters: Fairly little is known about coconut crabs, including their diet. Researchers found islands in the Pacific and Indian oceans with lots of the crabs had few ground-nesting birds, and those with lots of birds had no crabs. Since ground-nesting birds are very vulnerable to predators, it's possible voracious coconut crabs influence the distribution of these birds.

  • Coconut crabs are the largest land invertebrates — their legs can span up to a meter across, and they weigh as much as nine pounds. They have the strongest measured grip of any animal.
  • The crabs catch the birds with startling ease, according to Laidre. He watched a crab creep up a tree towards a sleeping bird and pounce, grabbing the bird by the wing and breaking it. The bird fell to the ground unable to fly, and the crab descended, and broke the other wing. Then, it held the bird in place with it's claws, and pummeled it with its legs.
  • The crabs have a keen sense of smell, and soon several others joined in on the feeding frenzy.
  • "It was pretty gruesome, they just converged on the bird and tore it apart," Laidre tells Axios.

Watch it happen: National Geographic, which funded Laidre's expedition, has a video of the crab massacre in action.

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