'Crazy ants' threaten Christmas Island crabs

Nick Squires, Telegraph 23 Dec 07;

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, a former British colony, is home to millions of bright red crabs but they are being threatened with extinction by an aggressive species of acid-squirting ant.

Yellow crazy ants have now halved the island's population of red crabs from 120 million to around 60 million since research began 15 years ago.

Scientists have discovered that the ants have spread out from isolated colonies and cover the entire island, which is administered by Australia but lies closer to Java.

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 in as little as two hours," said Laurie Corbett, an environmental consultant. "The ants then eat their insides out. They now cover the whole island."

The ants were accidentally introduced to Christmas Island in the 1930s, 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.

Mr Corbett found that the 12,000 hectare island is now infested with almost 80 super colonies, in which the ants are found at densities of 1,000 per square metre.

He said aerial spraying of the island in 2002 with 12 tons of poison had done little to halt the ants' advance.

The red crabs' annual migration from the island's forested interior to its rugged coastline in order to spawn has been described by Sir David Attenborough as one of the planet's greatest wildlife spectacles.

Christmas Island hopes 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 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," said Mr Corbett.

"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."

Mr Corbett accused the island's environmental managers of waiting too long before tackling the ant plague.

"They missed a good opportunity in the last 20 years to experiment with solutions, before the ants spread across the whole island."

But the manager of the Christmas Island national park, Mick Jeffery, said rangers were tackling the problem with the help of a £1.7m government grant.

"We are working on a new bait that is aimed at stopping the ants reproducing, and we are exploring promising bio-control options to disrupt a key food source."

He said "good progress" was being made in controlling the invasive insects. "Our targeted ant-baiting has helped keep red crab numbers relatively stable for the last five years."