Eleven years ago this column described the campaign by the Environment Agency to prevent the killer shrimp, Dikerogammarus villosus, from escaping from Grafham Water in Cambridgeshire. Extensive efforts were being made to get anglers and boat owners to sluice their kit before going to other rivers and lakes. Diddington Brook, the only outlet from the giant reservoir, was being filtered to prevent the shrimps getting to the River Ouse.
Sadly the attempt failed and what the agency calls the worst non-native invader of England and Wales’s waterways is now all over the country and impossible to control or eradicate.
Adults grow 3cm long, much larger than native shrimps, and earn their common name by killing water boatmen, damsel fly lava and even small fish, not necessarily to eat but just because they can. They also destroy the food supply of trout and wading birds, although many fish species will eat them too.
The shrimp originates in the Caspian Sea and has spread west across Europe through human-made canals and in the bilge water of boats. The species is extremely hardy and can stand water temperatures from freezing up to 30C, and live in any fresh or brackish water. Like so many other unwanted invasive species that arrived unintentionally, it is here to stay.