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An ant “empire” has been found stretching 6000 kilometres from Italy to Portugal. The supercolony of Argentine ants is thought to be the largest cooperative unit ever recorded, says Laurent Keller of the University of Lausanne in Proceedings of the National Academy of Sciences (early edition). The ants, which were introduced to Europe by accident in the 1920s, instantly accept genetically similar newcomers into nests even if they are from distant colonies. The empire’s reign is threatened, however, by a second supercolony of hostile ants that has established itself in eastern Spain.