Hairy crab versus crayfish in aquatic battle of Britain

It's the aquatic bout of the century. In the blue corner, all the way from the US, the lean, mean killing machine, the signal crayfish. And in the red corner, from China, the raging crustacean itself, the Chinese hairy crab, also known as the mitten crab.

As far as battles go, the looming showdown between two of Britain's most aggressive and successful alien invaders has got ecologists and conservationists in a lather, as the crab and crayfish armies come claw to pincer - very possibly in the River Lea in Enfield, north London.

'It's sort of an aquatic clash of the titans - perhaps the first time two species of alien invaders have battled it out for dominance on foreign soil,' said Philine zu Ermgassen, an aquatic ecologist at the University of Cambridge. 'Both species are very outgoing, charismatic creatures; big, omnivorous, and highly aggressive.'

Although ecologists expect the mother of all battles, none seems to care who wins. Instead, concern focuses on the growing list of invaders endangering domestic species.

The plight of the indigenous red squirrel is perhaps the best-known example, losing out a century ago to imported grey squirrels from North America and now pushed deep into Scotland. Fears focus too on the American mink, which escaped from fur farms and is pushing native water voles near extinction.

Plants, too, are causing ecological headaches, such as the Himalayan balsam, the giant hogweed, which can cause blisters to humans, the floating pennywort and the New Zealand pygmy plant, whose rampant sprawl crowds out natives and can block waterways, with huge implications for flood defences.