Crabs in the red
australia's Christmas Island is witness to a spectacular event every year. Millions of red crabs from this 134-sq km island's rainforest migrate to the sea to spawn, and then crawl back into their burrows. But now these crabs are being attacked by alien invaders. The threat is from supercolonies of crazy ants (Anoplolepis gracilipes), so called because of their irregular movements.
The red crabs of Christmas Island, 2,300 km from Perth, are vital for the ecosystem as they eat seedlings and leaves from the rainforest and help in litter breakdown. With the crabs dying, leaves and seedlings are accumulating and the whole forest ecosystem is breaking down in ant-invaded areas.
Says Mike Patrick, the conservator of parks, government of Australia: "The ants are blinding the crabs, attacking their joints and soft tissues and killing them.' Dennis O'Dowd of the Centre for the Assessment and Management of Biological Invasions, department of biological sciences at the Monash University, Melbourne, estimates that around three million of the island's 100 million red crabs have already been killed by these alien ants.
The supercolonies of "tramp' ants, which with their multiple queens and little
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