The coconut crab (Birgus latro)

Coconut crabs live in the Indian Ocean and the central Pacific Ocean, with a distribution that closely matches that of the coconut palm.[37] The western limit of the range of B. latro is Zanzibar, off the coast of Tanzania,[9] while the tropics of Cancer and Capricorn mark the northern and southern limits, respectively, with very few population in the subtropics, such as the Ryukyu Islands.[13] Some evidence indicates the coconut crab once lived on the mainland of Australia, Madagascar, Rodrigues, Easter Island, Tokelau, the Marquesas islands, and possibly India, but is now locally extinct in those areas.[13][1] As they cannot swim as adults, coconut crabs must have colonised the islands as planktonic larvae.[38]

Christmas Island in the Indian Ocean has the largest and densest population of coconut crabs in the world,[25] although it is outnumbered there by more than 50 times by the Christmas Island red crab (Gecarcoidea natalis).[39] Other Indian Ocean populations exist on the Seychelles, including Aldabra and Cosmoledo,[40] but the coconut crab is extinct on the central islands.[41] 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.[42]

In the Pacific, the coconut crab's range became known gradually. Charles Darwin believed it was only found on "a single coral island north of the Society group".[43] The coconut crab is far more widespread, though it is not abundant on every Pacific island it inhabits.[43] Large populations exist on the Cook Islands, especially Pukapuka, Suwarrow, Mangaia, Takutea, Mauke, Atiu, and Palmerston Island. These are close to the eastern limit of its range, as are the Line Islands of Kiribati, where the coconut crab is especially frequent on Teraina (Washington Island), with its abundant coconut palm forest.[43] The Gambier Islands mark the species' eastern limit.[9]