The non-native crayfish was first introduced to the UK in the late 1970s for aquaculture, but it soon began to spread.
Where the non-natives move in, the white claws are lost
Several different species now exist in the UK's waterways, but the signal crayfish (Pacifastacus leniusculus), which comes from North America, has so far caused the most damage - thanks, in part, to a disease it carries.
Ecologist Stephanie Peay told the BBC: "The plague does not seem to harm the non-natives, but if our native white-clawed crayfish [Austropotamobius pallipes] encounter it, they die within weeks."
Even if the non-native crayfish do not carry the plague, they still cause problems for the UK's white-clawed species.
Ms Peay describes the crustaceans as "aquatic thugs".
She explained: "Where the non-natives move in, the white claws are lost. Survey work has shown that it only takes between four and seven years from first arrival to achieve a complete local extinction.
"The only future for the white claws is in isolated water bodies that are completely free from non-native crayfish."
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