Invading Europe’s waterways: the crayfish occupation

An (invasive) signal crayfish, Pacifastacus leniusculus, crossing a road in Oxford.
Crayfish are freshwater crustaceans that can be found in a range of freshwater habitats, from fast-flowing rivers to swamps and ditches. Even in places where they are abundant, they are secretive and not commonly seen, so the ongoing widespread invasion by non-native crayfish species is unknown to many.
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