Argie invasion...this time it's ants

They came not from outer space, but from south America. In their billions they have silently and aggressively taken over great swathes of Europe.

It sounds like the creaking plot from a science fiction B-movie. But this is science fact: an immense "superstate" of ants from Argentina has united in Italy, France, Spain and Portugal to wage war on its domestic rivals.

With the confidence of a military general directing a campaign, the Argentine ants have established millions of nests in a "supercolony" stretching from Italy, through the south of France, around the coast of Spain and up the Atlantic coast of Portugal. It is thought to be the largest co-operative unit of individual organisms.

Faced with such a fearsome foe, perhaps no nation in Europe can feel safe - and soon only the Channel might stand between Britain and the tiny invaders sweeping across much of the Continent.

Wherever it goes in southern Europe the Argentine ant has managed to drive out the 20 or more indigenous species.

The Argentine immigrant was accidentally brought to Europe in the

Twenties, and started driving out domestic species. Linepithema humile has become one of the most persistent pests, raiding kitchens and protecting crop pests like aphids against chemical attacks from farmers.

"People have tried to treat them with pesticides but the best you can do is limit their numbers," said Laurent Keller, professor of ecology at the University of Lausanne in Switzerland.

Professor Keller, whose research is published today in the Proceedings of the National Academy of Science, said entomologists had never before noted such a huge supercolony of ants. "A collection of colonies acting as one can be described as a supercolony. It is very unusual because ants are usually highly aggressive," he said.

However, there is a glimmer of hope for the downtrodden domestic ants. A second, smaller supercolony of Argentine ants has been identified in the Catalan region of Spain and around Barcelona, and scientists say these ants are happy to make war on their compatriots.

"Aggression is extremely high between the two supercolonies," said Professor Keller.