On a small island in the Indian Ocean, a biologist filmed a coconut crab approach a sea gull that was dozing on a low branch and made it its next meal.
When you think about crabs, you probably think of the relatively harmless animals that wander about clicking their large claws without doing much harm to anyone. However, this might change when you see the scene filmed by biologist Mark Laidre from Dartmouth College in the United States that you can watch in the video above.
This specialist was conducting a study on a very strange animal: the coconut crab (Birgus latro). Able to grow up to a meter wide and weigh up to four kilograms, this animal has been awarded the title of being the largest land-dwelling arthropod in the world. They are found on islands in the Pacific and Indian oceans.
And yet, it’s not actually a crab so to speak, but rather belongs to the hermit crab family and can do some quite impressive things. It is able to climb trees that are several meters tall and break coconuts using its powerful pincers in order to eat the insides.
The behaviour that he observed was actually quite unexpected and shocking for Mark Laidre. In the middle of the night when he was on the Chagos archipelago, he stumbled upon a coconut crab going after a seabird, a red-footed booby, that was resting on a low branch. The arthropod grabbed the bird’s wing with one of its pincers before restraining it.
Despite the bird’s best efforts to fight back with its beak, it couldn’t and was quickly defeated. As if this scene wasn’t disturbing enough, about twenty minutes later, five other crabs arrived to compete for the feast while the bird was still alive.
‘As the booby lay paralyzed, the crabs fought, eventually tearing the bird apart,’ recalled Mark Laidre who revealed the video in a study published by the journal Frontiers in Ecology and the Environment.
A predator that influences its surrounding ecosystem
Coconut crabs are omnivores, so the fact that they eat meat is no surprise. The behaviour witnessed during the attack, however, is. But according to the biologist, it isn’t a first. He explained that one of his colleagues had already observed something similar two years ago: a crab dragging a bird into its lair.
Nevertheless, this study will allow the biologist to shed light on some doubts and queries linked to this environment. It seems that the presence of the Birgus latro has an effect on the nesting behaviour of birds on these small islands where they both live. Seeing as though coconut crabs can’t swim, they can’t leave or move between the islands in this archipelago. As a result, there is a lot more of them than in some places than in others.
However, Mark Laidre noted that where there is a larger population of this species, the birds don’t nest close to the ground. Now, this is understandable after seeing the threat this monstrous crab poses to them. The biologist now hopes to be able to continue his studies, particularly to find out whether these crabs regularly hunt birds.