The Christmas Island red crab is a species of land crab that is endemic to Christmas Island and the Cocos Islands in the Indian Ocean. Although restricted to a relatively small area, it has been estimated that 43.7 million adult red crabs once lived on Christmas Island alone, but the accidental introduction of the yellow crazy ant is believed to have killed about 10–15 million of these in recent years. Christmas Island red crabs are well known for their annual mass migration to the sea to lay their eggs in the ocean.
Like most land crabs, red crabs use gills to breathe and must take great care to conserve body moisture. Although red crabs are diurnal, they usually avoid direct sunlight so as not to dry out. Despite lower temperatures and higher humidity, red crabs are almost completely inactive at night. Red crabs also dig burrows to shelter themselves from the sun and will usually stay in the same burrow through the year.
During their annual breeding migration, red crabs will often have to cross roads, sometimes as many as 3 or 4, to get to their breeding grounds and then back to forest. As a result, red crabs are frequently crushed by vehicles and sometimes cause accidents due to their tough exoskeletons which are capable of puncturing tires. To ensure both the safety of crabs and humans, local park rangers work hard to ensure that the crabs can safely cross the island to the coast. Park rangers set up aluminum barriers called “crab fences” along heavily traveled roads.