Christmas Island red crab

How it lives

Red crabs live in the moist rainforest. They live about 12 years and mature at around 4 to 5 years of age. Each wet season, they walk to the sea to breed. The migration starts with the first heavy rain, usually in October or November but sometimes as late as December or January. Males arrive first and dig burrows. Females follow and spawn over about 5 to 6 nights near the last quarter moon, before dawn on a falling high tide, releasing up to 100,000 eggs each. The larvae spend about a month in the sea, and the tiny crabs then come ashore and climb to the forest. Most larvae are eaten, and large numbers survive only once or twice a decade.

Where it goes

Adults make a round trip each wet season between the inland forest and the shore, timed by rain, moon and tide. Young crabs make the trip up from the coast, reported at about 9 days to reach the island's centre. The exact dates change every year.

We only draw a journey on the map when scientists have tracked it or clearly documented it. For this animal we have not found one yet.

Populations

Christmas Island is the only place the species lives. Parks Australia says the island has more than 100 million red crabs. An earlier estimate cited by Wikipedia put the adult population at about 43.7 million, so the figures differ by source and method. Yellow crazy ants, an invasive species, killed an estimated 10 to 15 million crabs, and tens of millions of land crabs since the late 1990s according to Parks Australia. A biological control project using a tiny wasp is under way: lac scale insects have been reduced, but the effect on the ants is still uncertain. The IUCN has not assessed this species (GBIF record, 2026).