Hunt for 'killer' shrimp first found in Cambridgeshire
The hunt is on for a shrimp, dubbed "killer" because of its appetite, which is threatening river wildlife.
Traps baited with cat food and fish food are being used to detect the dikerogammarus villosus shrimp, the Environment Agency said.
The shrimp first found in Cambridgeshire can grow to 1.2in (3cm), much bigger than native shrimps.
Scientists aim to ensure no populations go undetected so more than 100 traps are to be set in "high priority" sites.
The Dikerogammarus villosus shrimp, which has gained the nickname "killer" as a result of its voracious appetite, has spread rapidly through Europe in recent years from the Black and Caspian seas.
It was first discovered in England at Grafham Water near Huntingdon last autumn.
Within weeks it had also turned up at Cardiff Bay and Eglwys Nunydd reservoir in Port Talbot.
The species preys on native wildlife such as damselflies and water boatmen and poses an indirect threat to other animals which feed on them.
Strict measures requiring boaters and anglers to thoroughly clean and dry all equipment before and after use were immediately put into place at the three sites where the shrimp has been found.
Paul Raven, heading a task force tracking down the invader, said: "This shrimp may be small but it poses a big threat to native wildlife in our rivers, lakes and streams.
"Native freshwater shrimps, damselflies and water boatmen could be particularly at risk, with knock-on effects on the species which feed on them.
"Since the first discovery at Grafham, our focus has been on containing it through effective biosecurity measures and investigating how far it might have spread.
"Extensive monitoring of rivers, reservoirs and lakes has not uncovered any new colonies but trapping will now be used to help ensure no invasive shrimp populations go undetected."