Science behind why millions of Red Crabs march together in Christmas Island

Science behind why millions of Red Crabs march together (Image: Canva)

A sea of scarlet sweeps across Christmas Island every year. Millions of red crabs leave their forest burrows and head to the coast. Their goal is reproduction which is a journey guided by rain, moon and tide.

A Forest in Motion

The red crabs live deep within the island’s tropical rainforest. When the wet season begins, they emerge in waves. The males lead, carving paths through rocks and roads. Females follow later, heavy with eggs.

The migration is perilous under the tropical heat. Crabs travel during cooler hours to avoid dehydration. They rest in shade, conserving moisture as they cross miles of terrain. Local authorities even close roads to protect their passage.

Moonlit Spawning Spectacle

The arrival of crabs at the coast is timed perfectly. Spawning occurs during the last quarter of the moon. Females release up to 100,000 eggs into the sea. The larvae drift with the currents, developing far from shore.

After weeks adrift, surviving juveniles return to land. They march inland, repeating the same life cycle. This mass return ensures the island’s crimson tide will rise again.

Nature’s Clockwork Wonder

The migration is one of Earth’s great natural events. It shows nature’s precise timing and the resilience of life. Conservation measures, like crab bridges, help protect this delicate ritual.