What is the name of the annual mass migration of red crabs on Christmas Island?

The annual mass migration of Christmas Island’s red crabs is called the red crab migration. Millions of Gecarcoidea natalis leave the island’s rainforest and travel toward the coast to breed and release their eggs into the ocean.

The migration usually begins with the wet season, commonly in October or November, and its exact timing is linked partly to rainfall and the phases of the Moon. Males generally reach the coast first. Females later remain near the shore to incubate their eggs, releasing them into the sea at a precisely timed high tide.

The spectacle can last one to two weeks and is so large that roads are closed or fitted with barriers and underpasses. The crabs’ journey is not simply a march to the beach: after hatching, their larvae spend several weeks at sea before young crabs return to land. They eventually grow in the forest and begin joining the migration when they reach maturity.

The phrase is sometimes confused with migrations of coconut crabs or other red crab species, but this famous event specifically concerns Christmas Island’s endemic land crab.