The invaders destroy up to 95% of these native white-clayed crayfish

Introduced in the 1970s to fish farms and ornamental ponds, the crayfish escaped and colonised rivers up and down the country.

For seven years, the Environment Agency has trapped and destroyed thousands of signal crayfish on the Stour as part of a plan to save the native white-clawed crayfish, which has already been lost in some areas of Britain.

Crayfish trapper Dan Hayter told BBC Look East: "They carry a plague, and our native crayfish have no immunity to it.

"If there are signal crayfish in the same water, even if they haven't come into contact with one another, they struggle to survive."

Kirk Markham baits his crayfish traps with ripe bananas

Upper reaches of the Stour are already infested, and Mr Hayter and colleague Kirk Markham have a mission - to prevent the aliens from reaching the last surviving pockets of native crayfish on other rivers nearby.

Mr Markham said: "They generally compete with each other for breeding space, food, and females to mate with, and they are quite aggressive.

"They're also cannibalistic, and they don't really mind what they eat."

He said trappers have taken to capturing them using bananas as bait.

"It's a lot nicer putting bananas in the traps instead of old fish," said Mr Markham.