Update: Reader Dennis Hansen, a biologist who works on the Indian Ocean island of Aldabra in the Seychelles, which (like the Galapagos) has giant tortoises, sends three coconut crab photos and a note:
Here’s a few photos of coconut crabs from Aldabra, for your perusal. They leave the giant tortoises alone, it seems. At least until a tortoise dies, by which time the crabs tear it apart from the inside. When staying in one of the remote field camps on the atoll, they do what they can to rob us of our meagre field rations, though. Don’t leave food on the table, or it will disappear within a few minutes.
“These animals are known locally as robber crabs on their native Christmas Island because they have a reputation for curiosity and for stealing things. They wander into unlocked houses and steal knives, forks and even shoes.”
Actually, I know these beasts by the name “coconut crab,” but their scientific name is Bigus latro (“Bigus” is right!). According to Wikipedia, it’s the largest land-living arthropod in the world, and can weigh up to 4.1 kg (9 pounds). (Question for readers: what is the largest living arthropod among all animals?) And they can live for up to 60 years!
While they’re reputed to climb trees and pick coconuts, they don’t appear to do that often, though they can open coconuts “collectively” or, individually, with great effort. Instead, their usual diet consists of fruit, nuts, seeds, and tree pith.
They’re terrestrial hermit crabs, but only the juveniles use shells, and their geographic distribution is shown on the map below. Wikipedia notes:
Coconut crabs live in the Indian Ocean and the central Pacific Ocean, with a distribution that closely matches that of the coconut palm.
Christmas Island in the Indian Ocean has the largest and densest population of coconut crabs in the world, although it is outnumbered there by more than 50 times by the Christmas Island red crab, Gecarcoidea natalis. Other Indian Ocean populations exist on the Seychelles, including Aldabra and Cosmoledo, but the coconut crab is extinct on the central islands.Coconut crabs occur on several of the Andaman and Nicobar Islands in the Bay of Bengal. They occur on most of the islands, and the northern atolls, of the Chagos Archipelago.
Since they drown easily, one wonders how they got to all those islands. Perhaps a reader can enlighten us.
And the crabs are both smart and tenacious when it comes to getting coconuts:
It is a common perception that the coconut crab cuts the coconuts from the tree to eat them on the ground. The coconut crab can take a coconut from the ground and cut it to a husk nut, take it with its claw, climb up a tree 10 m (33 ft) high and drop the husk nut, to access the content inside.They often descend from the trees by falling, and can survive a fall of at least 4.5 metres (15 ft) unhurt. Coconut crabs cut holes into coconuts with their strong claws and eat the contents, although it can take several days before the coconut is opened.
Thomas Hale Streets discussed the behaviour in 1877, doubting that the animal would climb trees to get at the nuts. In the 1980s, Holger Rumpff was able to confirm Streets’s report, observing and studying how they open coconuts in the wild. The animal has developed a special technique to do so: if the coconut is still covered with husk, it will use its claws to rip off strips, always starting from the side with the three germination pores, the group of three small circles found on the outside of the coconut. Once the pores are visible, the coconut crab will bang its pincers on one of them until they break. Afterwards, it will turn around and use the smaller pincers on its other legs to pull out the white flesh of the coconut. Using their strong claws, larger individuals can even break the hard coconut into smaller pieces for easier consumption.
Here’s a video of one carrying his coconut prize:
This largest of all crabs is called a Coconut or Robber Crab. The Coconut Crab, Birgus latro, was found after dark on an unpaved country road on Christmas Island, Australia. It is seen here carrying a coconut. However, it also eats a large variety of other items, including dead crabs. . The headlights of a car serve as illumination here.
A photo of one attacking a coconut. What a beautiful animal! I must confess, though, that when I look at those claws I think of drawn butter (they’re apparently edible, but I wouldn’t eat one as they’re endangered when in contact with humans).
Here’s a monster, with a LOLzy Youtube comment after the video:
A few more Coconut Crab Facts:
Coconut crabs are considered one of the most terrestrial decapods, with most aspects of its life linked to a terrestrial existence; they will drown in sea water in less than a day.Coconut crabs live alone in underground burrows and rock crevices, depending on the local terrain. They dig their own burrows in sand or loose soil. During the day, the animal stays hidden to reduce water loss from heat. The coconut crabs’ burrows contain very fine yet strong fibres of the coconut husk which the animal uses as bedding. While resting in its burrow, the coconut crab closes the entrances with one of its claws to create the moist microclimate within the burrow necessary for its breathing organs. In areas with a large coconut crab population, some may come out during the day, perhaps to gain an advantage in the search for food. Other times they will emerge if it is moist or raining, since these conditions allow them to breathe more easily. They live almost exclusively on land, returning to the sea only to release their eggs; on Christmas Island, for instance, B. latro is abundant 6 kilometres (3.7 mi) from the sea.
Should a coconut crab pinch a person, it will cause pain and be unlikely to release its grip. Thomas Hale Streets reports a trick used by Micronesians of the Line Islands to get a coconut crab to loosen its grip: “It may be interesting to know that in such a dilemma a gentle titillation of the under soft parts of the body with any light material will cause the crab to loosen its hold.”