Several American animals, such as ruddy ducks, mink, otters and crayfish - have established beachheads on British territory and their rapacious ways are threatening to destroy many native species who cannot compete with them in the struggle for survival.
The most voracious hunter of all is the American mink which has built up a formidable wild population in the British countryside since it first escaped from mink farms in the Twenties, David MacDonald of Oxford University told the association.
"American mink are a triumph of adaptability and opportunism in their success. They are perhaps the most successful mammal carnivores one can think of. Not only have they been causing problems in this country, but in many other areas of the world where they have been introduced," Dr MacDonald said.
The American mink is wiping out the native water vole because it can attack them in their burrows or in the water.
Ruddy ducks, whose males mate with more than one female, are breeding with the European white-headed duck, whose population has declined from around 100,000 in the Thirties to only 5,000.
"The ruddy duck is more aggressive and less demanding in its habitat requirements. Unchecked, it is likely that the ruddy duck will completely absorb the white-headed duck population," Dr Baz Hughes, head of wildfowl conservation at the Wildfowl and Wetlands Trust, said.
American crayfish are running riot in British waterways, where they first became established in the Seventies. Since then they have outwitted and eaten the smaller, native crayfish and are even destroying riverbanks by burrowing into them.
Their claws are powerful enough to remove a finger, said Dr David Holditch of the University of Nottingham.
Morris Gosling, of the Zoological Society of London, said the introduction of foreign species has become one of the most important factors influencing extinction rates.Reuse content