KEY POINTS:
The festive season holds little cheer for the most famous inhabitants of Christmas Island, a subtropical speck in the middle of the Indian Ocean.
The tiny outcrop is home to millions of bright red crabs but they are being threatened with extinction by a species of acid-squirting ant.
In the past 15 years, yellow crazy ants have halved the Australian-owned island's population of red crabs from 120 million to around 60 million.
Scientists have now discovered that the ants have spread out from isolated colonies and cover the entire island, which lies closer to Java than Australia.
Crazy ants kill the crabs by spraying them with formic acid. "It makes the crabs blind, they start frothing at the mouth, and they die within two hours," environmental consultant Dr Laurie Corbett said yesterday. "The ants then eat their insides out."
The ants were accidentally introduced to Christmas Island a century ago, possibly in shipments of timber, but it was only in the 1990s that they became a serious problem, after the evolution of multi-queened super colonies.
Corbett found that the 12,000ha island is now infested with almost 80 super colonies, in which the ants are found at densities of 1000 per square metre. Aerial spraying of the island in 2002 with poison has done little to halt the advance.
The red crabs' annual migration from the islands forested interior to its rugged coastline in order to spawn has been described as one of the planet's greatest wildlife spectacles.
Christmas Island hoped to turn the migration into a major tourist attraction, as its main source of income - phosphate mining - comes to an end.
Earlier this year the Australian federal Government rejected an application for the extension of the island's phosphate mine on the grounds that it would destroy forest and threaten endangered species, including the red crab.
But unless drastic measures are taken to exterminate the ant super-colonies, the crabs could be doomed.
"Crazy ants are very difficult to control, so there's a pretty good chance that the crabs could become extinct or at least be reduced to very low numbers.
"That would be catastrophic for the island because crabs are a keystone species. They chew up the rainforest floor and deposit nutrients back into the soil. The ecology of the rainforest depends entirely on the crabs."
Christmas Island's unique flora and fauna are also at grave risk from other introduced species, from feral cats and wild chickens to giant African snails.
