Adult coconut crabs feed primarily on fleshy fruits, nuts, seeds, and the pith of fallen trees, but they will eat carrion and other organic matter opportunistically.

Anything left unattended on the ground is a potential source of food, which they will investigate and may carry away – thereby getting the alternative name of "robber crab".

Mating occurs on dry land, but the females return to the edge of the sea to release their fertilized eggs, and then retreat up the beach.

The larvae that hatch are planktonic for 3–4 weeks, before settling to the sea floor, entering a gastropod shell and returning to dry land.

In the 3–4 weeks that the larvae remain at sea, their chances of reaching another suitable location is enhanced if a floating life support system avails itself to them.

Examples of the systems that provide such opportunities include floating logs and rafts of marine or terrestrial vegetation.

[12][13] Reports of its size vary, but most sources give a body length up to 40 cm (16 in),[14] a weight up to 4.1 kg (9 lb), and a leg span more than 0.91 m (3 ft),[15] with males generally being larger than females.

Absent the physical constraint of living within another creature's shell B. latro grows much larger than its relatives in the family Coenobitidae.

[17] The hardened abdomen protects the coconut crab and reduces water loss on land, but must be periodically moulted.

This organ can be interpreted as a developmental stage between gills and lungs, and is one of the most significant adaptations of the coconut crab to its habitat.

[23] Coconut crabs use their hindmost, smallest pair of legs to clean these breathing organs and to moisten them with water.

The organs require water to properly function, and the coconut crab provides this by stroking its wet legs over the spongy tissues nearby.

Crabs that live in water have specialized organs called aesthetascs on their antennae to determine both the intensity and the direction of a scent.

[25] While insects and the coconut crab originate from different clades, the same need to track smells in the air led to convergent evolution of similar organs.

[27] Coconut crabs mate frequently and quickly on dry land in the period from May to September, especially between early June and late August.

[34] Upon reaching the glaucothoe stage of development, they settle to the bottom, find and wear a suitably sized gastropod shell, and migrate to the shoreline with other terrestrial hermit crabs.

[18] They grow remarkably slowly, and may take up to 120 years to reach full size, as posited by ecologist Michelle Drew of the Max Planck Institute.

[39] Other Indian Ocean populations exist on the Seychelles, including Aldabra and Cosmoledo,[40] but the coconut crab is extinct on the central islands.

[9] The diet of coconut crabs consists primarily of fleshy fruits (particularly Ochrosia ackeringae, Arenga listeri, Pandanus elatus, P. christmatensis); nuts (Aleurites moluccanus), drupes (Cocos nucifera) and seeds (Annona reticulata);[44] and the pith of fallen trees.

[44] During a tagging experiment, one coconut crab was observed killing and eating a Polynesian rat (Rattus exulans).

[48] In 2016, a large coconut crab was observed climbing a tree to disable and consume a red-footed booby on the Chagos Archipelago.

[54] Coconut crabs are considered one of the most terrestrial-adapted of the decapods,[55] with most aspects of its life oriented to, and centered around such an existence; they will actually drown in sea water in less than a day.

Its large size and the quality of its meat means that the coconut crab is extensively hunted and is very rare on islands with a human population.

[57] The coconut crab is eaten as a delicacy – and regarded as an aphrodisiac – on various islands, and intensive hunting has threatened the species' survival in some areas.

[58][59] On the Nicobarian Kamorta Island, it is believed that eating the crab leads to bad luck and can cause severe, sometimes fatal, illnesses.

In cases where a local falls ill after consuming the crab, their family creates a wooden replica of the creature.

[63] A popular internet meme suggests that Amelia Earhart crash-landed on Nikumaroro and her remains were rapidly consumed by coconut crabs on the island.

[67][68] Coconut crab populations in several areas have declined or become locally extinct due to both habitat loss and human predation.

[71] In the Northern Mariana Islands, hunting of non-egg-bearing adults above a carapace length of 76 mm (3 in) may take place in September, October, and November, and only under license.