When and why do the Christmas Island crabs migrate?

On the small Australian island located in the Indian Ocean, every year on Christmas Island during the rainy season, tens of millions of red crabs move from the inland to the coast to reproduce and lay eggs. This is one of the most impressive animal migrations ever seen.

What is the time of migration of a red crab?

Red crabs live alone in dirt burrows, or deep rock crevices. Crabs stay in the shade of their dwelling for most of the year. In October or November, when the wet season is about to return, crabs begin their migration to the shore. This timing coincides with the lunar cycle and the tides.

Do crabs migrate or hibernate?

Crabs do not hibernate, rather they lie dormant for the long winter (usually from November through May.)

What happened to the crabs on Christmas Island?

Adult red crabs have no natural predators on Christmas Island. 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 (one-quarter to one-third of the total population) in recent years.

How do crabs know when to migrate?

The exact timing and speed of the migration is determined by the phase of the moon. Red crabs always spawn before dawn on a receding high-tide during the last quarter of the moon. Incredibly, they know exactly when to leave their burrows to make this lunar date.

How much shorter has the crabs winter dormancy period become since the 1930s?

Water in the Chesapeake has already warmed so much that crabs’ winter dormancy period in Maryland has shrunk by about a month since the 1930s.

Why Christmas Island has so many crabs?

Christmas Island’s mass red crab migration is one of the most incredible natural processes on Earth. Every year, millions of these large crabs emerge from the forest and make their way to the ocean to breed, swarming across roads, streams, rocks and beaches.