Tens of millions of red crabs live on the Christmas Island which is an Australian territory in the Indian Ocean lying south of Java, Indonesia.
Most of Christmas Island’s adult red crabs begin their breeding migration to the sea as soon as the wet season rains have established. But we can never be sure when the wet season is going to begin.
This is one of the most famous events in the World and to reduce the number of crabs killed by vehicles during the migration, ‘crab crossings’ are being constructed in roads which cross main crab migration paths.
The crabs’ breeding timetable is fixed around the phases of the moon. Spawning – the dropping of their eggs into the sea must occur before sunrise on spring tides during the last quarter of the moon, regardless of any other factor. The timing of spawning is the only certain and predictable part of the whole migration, all other stages of the migration will vary with the prevailing weather.
The crabs will start their migration if there is enough time for them to complete their downward migration, mate and develop eggs before the next suitable spawning date.
