They're using coconuts...

Andrew Hosie's blog | Created 4 years ago

A large land crab, which climbs trees and feeds on coconuts, can hardly go unnoticed. Vague reports date back to the 9th century, and include descriptions by Charles Darwin and Carolus Linnaeus. According to these early records Birgus latro was once widespread throughout the Pacific and Indian Ocean, mirroring the distribution of coconut palm trees.These coconut or robber crabs, however, are considered a delicacy and aphrodisiac in some cultures, and as a result they are now restricted to islands scarcely inhabited by humans, where they have nocturnal and shy habits. Not on Christmas Island, however. There, the world’s largest population of coconut crabs has developed particular behaviours such as also being active during the day (when humidity levels are high) and congregating to feed, generally under fruit trees. This is where this particular specimen was collected back in 1969.

The Coconut crab.

Birgus latro is the largest terrestrial crustacean, weighing up to 4 kg and growing up to 1m in length from leg to leg. They still depend on water to spawn and for the initial larval stages, but are highly adapted to live on land: they cannot swim, they mate on land and their sensory systems are adjusted to terrestrial life. But the main adaptation is the presence of lung-like structures, which enable them to breathe air. In less than a day they would drown if left in seawater.

Coconut  crabs are actually a species of hermit crab. However, they only use a shell (or piece of broken coral) to protect their abdomen during early life stages. As adults they develop a hard skeleton over the whole body. B. latro reaches sexual maturity at about 5 years and can live to 60 years.

Coconut crabs caught in action.

Coconut crabs are omnivorous, feeding on fruit, nuts, scavenging and even feeding on other coconut crabs. They are famous for opening and feeding on coconuts, but this is not the main item on their diet. Opening a coconut requires special techniques, and opening a nut can take several days and is usually a collective achievement. Their incredible ability to climb trees (up to 10m) has been described as a mechanism to reach food, and also a protection strategy, to escape predators. Apparently their ability to descend from trees is not as impressive, and they generally drop down. They can survive falls of up to 4.5m unharmed.

Populations of B. latro have been locally extinct, and the species is currently under the ‘data deficient’ category under the IUCN red list.