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Marching Crabs

Story: Marching Crabs
Episode: 5
Presenter: Trevor Cochrane
Air Date: 13th December 2020

The red crab is a species that is endemic to Christmas Island and their annual migration is one of the most remarkable natural events on the planet.

  • The island receives the first rains for the season around October and November. These trigger the mass migration of the red crabs.
  • Approximately 60 million red crabs undertake what is called downward migration, where they make their way down to the coast to mate.
  • The male digs a burrow, which is where mating will take place. After a few days, the female is ready to release her eggs into the ocean.
  • The average female produces more than a hundred thousand eggs each year.
  • Christmas Island’s biodiversity is unique, having developed in isolation over millions of years. The red crab is vital to the total ecosystem’s health.
  • Their biggest threat is the introduction of foreign species, like the yellow crazy ant. These ants sprayed formic acids over the crabs, blinding and eventually killing them.
  • National Parks are trialling a biological control for the yellow crazy ant, which has seen red crab numbers return to normal.

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