Story: Marching Crabs
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.
For more information, head to