Appearance
The carapace is up to 116 millimetres wide, rounded, and encloses the gills. The claws are usually of equal size, unless one becomes injured or detached, in which case the limb will regenerate. The male crabs are generally larger than the females, while adult females have a much broader abdomen and usually have smaller claws.Distribution
Early inhabitants of Christmas Island rarely mentioned these crabs. It is possible that their large population size was caused by the extinction of the endemic Maclear's Rat, ''Rattus macleari'' in 1903, which may have controlled the crab's population. Surveys have found a density 0.09–0.57 adult red crabs per square metre, equalling an estimated total population of 43.7 million on Christmas Island. Others have estimated that about 120 million are found on this island, but the basis for that claim is unclear.An exploding population of the yellow crazy ant, an invasive species accidentally introduced to Christmas Island and Australia from Africa, is believed to have killed 10–15 million red crabs in recent years. In total , the ants are believed to have displaced 15–20 million red crabs on Christmas Island.
Habitat
Christmas red crabs live in burrows for shelter from the sun. Since they breathe through gills, the possibility of drying out is dangerous. They are famous for their annual migration to the sea to lay their eggs in the ocean.References:
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