Alien Species

The introduction of non-native species to these islands has been a mixed blessing. Some species have not thrived while others have overwhelmed their native counterpart. The new world grey squirrel is one such example. Our rivers have also received some unwelcome visitors, some of which have thrived.

Here is the Environment Agency's list of top ten least favourite alien species:

1 Japanese Knotweed Plant Fallopia japonica
2 North American signal crayfish Crustacean Pacifastacus leniusculus
3 Mink Mammal Mustela vison
4 Giant Hogweed Plant Heracleum mantegazzianum
5 Floating pennywort Plant Hydrocotyle ranunculoides
6 Himalayan Balsam Plant Impatiens glandulifera
7 Australian swamp stonecrop Plant Crassula helmsii
8 Canadian pondweed Plant Elodea canadensis
9 Parrots feather Plant Myriophyllum aquaticum
10 Topmouth gudgeon Fish Pseudorasbora parva

From the list above there are five species currently doing rather well on our river banks marked in red. Projects are in hand to contain or eradicate the worst of them. Please see Projects.

Japanese KnotweedSignal Crayfish

MinkGiant Hogweed

Himalayan BalsamDikerogammarus villosus – the Killer shrimp.