Some of Britain's best loved wildlife, including bluebells, red squirrels and water voles, are threatened by invasive species. The red squirrel has suffered since the introduction in the 19th century of the stronger, more adaptable, grey squirrel

Red-eared terrapins, originally from the US, are foot-long former pets that can terrorise ducklings

Some invaders pose a risk to human health, like this giant hogweed, whose sap causes blistering