large, nocturnal land crab of the southwest Pacific and Indian oceans. It is closely related to the hermit crab and king crab. All are decapod crustaceans (order Decapoda, class Crustacea). Adults are about 1 m (about 40 inches) from head to tail and weigh about 4.5 kg (10 pounds). The full-grown adult crab ranges in colouring from light violet to brown and deep purple. Young adults are brown, with black stripes on their legs. The crab uses two large chelae, or pincers, to pound or chip open coconuts—the soft white meat of which is its principal diet. Although robber crabs can climb trees, they apparently eat only coconuts already on the ground.

The female releases her ripe eggs in the sea, and they immediately hatch as microscopic, swimming zoeas. This first larval stage, which lives in the water, feeds on small organisms. After 20 to 30 days the zoea develops into a glaucothoe, the intermediate stage, and leaves the water to live in a seashell for three or four weeks. It then discards the shell, buries itself in moist sand, and transforms into a small adult. Most of the daylight hours are passed in burrows up to about 0.6 m (2 feet) deep, sometimes two crabs to a burrow. The crabmeat is a local delicacy.