Christmas Island Red Crab

Gecarcoidea natalis, the Christmas Island red crab, is a terrestrial crab in the family Gecarcinidae, formally described by Pocock in 1888, endemic to Christmas Island and the Cocos (Keeling) Islands in the Indian Ocean. Adults display prominent red colouring, though some appear orange or, rarely, purple, and their carapace reaches up to one hundred sixteen millimetres wide; males tend to be larger than females, while females have broader abdomens and smaller claws. An estimated forty three million seven hundred thousand adult red crabs once lived on Christmas Island alone, though the population has declined sharply since the accidental introduction of yellow crazy ants, believed to have killed ten to fifteen million red crabs, roughly a third of the total. Each year during the wet season, typically October or November, the crabs undertake a mass migration to coastal breeding grounds, with millions emerging at once to carpet the ground, prompting authorities to close roads and install aluminium barriers and dedicated crab crossings to protect them.