Photo: Gerald Zinnecker all rights reserved
If you are indoors when it happens, the first thing you notice is the crackling noise, a chorus of clicking. The march has begun. Looking outside, the sight beggars belief: the entire forest floor, and even the roads that run through it, swathed in a sea of red. So thickly do the crabs blanket the routes to the shoreline that they can easily be seen from air. What we are witnessing is the annual migration of the red crabs – one of the most spectacular animal migrations on the planet.
Photo: J Jaycock, Australian Government Attorney-General’s Department, copyright Commonwealth of Australia reproduced by permission
Human help: Red crabs confront a ‘crab barrier’ to cross a road
Christmas Island in Southeast Asia sets the stage for this most epic of nature’s journeys: the synchronised mass movement of 65 million crabs walking up to 8 km in just 5 days. When the wet season kicks in, and the tide is right, the crabs make their move, emerging from their solitary burrows in the tall rainforest, and walking as one to the sea. Nothing gets in the way of these single-minded crustaceans, neither shops, nor golf course nor busy roads. Even cliff faces are climbed down with apparent ease.
Photo: © CITA
As one: Red crabs at Christmas Island’s blow holes
The millions of bright red crabs that set off each year – normally in October or November – are driven by a clear purpose: to breed and spawn. When the broad columns arrive at the beaches, following their well-trodden routes, the males leading the way first rehydrate in the sea, then retreat to the lower terraces to dig and fight over burrows. The greater numbers of females soon follow and mating takes place, usually in the privacy of the burrows for which the males have fought so hard for possession.