The immense Coconut Crab (or Robber Crab) is the largest terrestrial arthropod on earth, (Grub 1971). They have been found to attain weights in excess of 5kg (Fletcher & Amos 1994) and can span over 50cm from claw to claw, (Reyne 1939). They are very powerful creatures and have vastly strong pincers. These ‘chelae’ can easily cut through an ordinary broom handle, (Johnson 1965).

(Adult Birgus - Website 9)

The Coconut Crab comes from the same family as the hermit crab. The family Coenobitidae contains only two genera Coenobita, the land-hermit-crabs, and Birgus, containing only the Coconut Crab, Birgus latro, (Johnson 1965). Although the two genera appear very different in adulthood, they share extremely similar juvenile lives. Like adult land hermit crabs, the Coconut Crab occupies an old snail shell when it is young. Eventually, it gets so big that it cannot find any suitable shells. It then undergoes metamorphosis into the adult form, (Harms 1932).

(A Hermit Crab occupying a plastic bottle top as a substitute shell - Website 15)

As an adult, Birgus look very peculiar. They are easily recognised by their spider like abdomen, which is hard and dull coloured above but soft and brilliantly coloured below, (Johnson 1965). The crab occurs in two different colour phases, a blue and a red (Grubb Harms 1971). From the front, the Coconut Crab still appears very similar to a hermit crab. However hermit crabs have special hind-legs adapted for gripping onto their adopted shell. In adult Coconut Crabs, this last pair of legs has become greatly reduced, (Johnson 1965). The next pair has become readapted for walking and is used to help the crab climb trees.

(Adult Birgus decending a tree)

The Coconut Crab lives almost exclusively on small tropical islands. The wide distribution across the tropical regions of the Indo-Pacific covers a region of 180° longitude, (Reyne 1939). The crab is also present outside the tropics on islands washed with tropical warm currents. An example is the Ryu Kyu Islands of Japan, which are washed by the warm Japan Stream, (Reyne 1939). Birgus is also found in the Indian Ocean on islands such as Aldabra and Christmas Island, (Reyne 1939). The crabs have become so widespread due to the fact that they spawn in the sea. The currents can then carry the larvae many miles and propagate new populations on new islands, (Harms 1932).

(Hoga Island)

Despite this wide distribution, the Coconut Crab is threatened with extinction. In remote regions, the crab has become a valuable cash crop. It is considered a delicacy and is eaten privately or sold in restaurants. Intensive harvesting in combination with the ease of capture has resulted in its red-listed status and in some countries the crab is already virtually extinct, (Fletcher & Amos 1994). The aim of this site is to promote interest in the Coconut Crab and aid its recovery from the brink of extinction. Click on the links to find out more.