What is a Coconut Crab?

Debra Durkee

The coconut crab is a monstrous crab that reaches sizes unheard of among other arthropods. Found on islands in the Indo-Pacific Ocean, it was one of the species recorded by Charles Darwin on his legendary expeditions. Specimens can easily reach up to 3 feet (1 m) in diameter and weigh as much as 11 pounds (5 kg), with the females being considerably smaller than males.

The coconut crab was one of the species recorded by Charles Darwin on his legendary expeditions.
The coconut crab was one of the species recorded by Charles Darwin on his legendary expeditions.

Actually a type of hermit crab much like the tiny ones kept as pets, the adult coconut crab does not share other hermit crabs' habit of using a series of shells as armored, mobile homes. Instead, the body of the coconut crab itself develops into a hard, shell-like coating, which does not limit growth and allows it to reach its massive size. The name coconut crab comes from the crab's ability to crack open and eat coconuts with its strong claws. Pressure from the claws can move or pick up objects as heavy as 60 pounds (28 kg). The coconut crab can be a variety of colors from red to purple to blue; color depends on what island it is from.

For most of their lives, these crabs live along the coastlines of the islands they inhabit. During breeding season, crabs head into the jungle in order to mate. Afterward, the female heads out into the sea to lay her eggs. There, the eggs quickly hatch and remain in the water until the young crabs grow legs and mature enough to make it to land.

Young coconut crabs use shells for protection, much like their smaller relatives, but they stop using them when they are between two and three years old. A coconut crab reaches breeding age around five years of age, and during this time it regularly sheds its hard, outer exoskeleton as it grows. It stops growing when it is about 40 years old, but can live for decades beyond that.

Coconut crabs are also unique because while they breathe with the help of gills that must be kept damp, they can also drown in water. Better suited to life on land, they almost always remain in close near the sea, where eggs are released. A largely nocturnal creature, they can easily travel with their strong legs and powerful claws, and spend the day hiding in rock shelters or dead trees.

Viewed by many as a curiosity, coconut crabs have been threatened by the arrival of tourists and the development of a food industry to supply consumers who consider them a delicacy and, in some places, an aphrodisiac. Expanding cities and the establishment of tourism-related developments have intruded on the crabs' natural habitats, and they are preyed on by some animals introduced by human visitors to their islands. While some islands maintain thriving populations, the strain is clearly visible on the crabs that inhabit other islands.

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