Well, that escalated quickly...
The largest land dwelling crab in the world, the coconut crab or Birgus latro is more than just their name. Other than weighing up to 4 kilograms, capable of reaching around a meter across, and being opportunistic scavengers, a recent video shows how these land crabs can kill a large, back-boned animal: a common seabird, the red-footed bobby.
Around early 2016, Dartmouth College researcher Mark Laidre visited a series of atolls just south of India called the Chagos Archipelago. The area has a lot of coconut crabs, so encounters with the land crustacean are common. Laidre spotted a crab slowly climbing a tree to stalk a seabird which was sleeping in a nest just a few feet off the ground, and so he started to get his camera ready.
And in a blink of an eye, the coconut crab suddenly pinches one of the bird’s wings, breaking the bone within and causing it to fall to the ground. After that, the crab went down to the fallen bird and broke the other wing with its claws. “At that point, when both its wings were broken and it was on the ground, it couldn’t go anywhere,” says Laidre. Not long after that, five other crabs went to the bird and started to tear it apart and eat it. “It was pretty gruesome,” Laidre says.
A coconut crab is really strong, with its force up to 3300 Newtons, according to data from Shin-ichiro Oka at the Okinawa Churashima Foundation Research Center in Japan. “The claws of coconut crabs can generate a force 80 to 100 times the mass of their body,” says Oka. “The crab in the video seems to be about 2 kilograms, so it would be able to easily break the bird’s bones.” The force is comparable to a bite force of a lion.
If this phenomenon is more common than we thought, seabirds may mostly be absent in an island inhabited by coconut crabs. “In areas where these guys are present and abundant, it would be a smart move, especially among ground-nesting birds, not to place eggs there,” Laidre says.
Get weekly science updates in your inbox!