Signal crayfish

Pacifastacus leniusculus

Origin: North America

Route of introduction: Introduced to the UK in the late 1970s as a food source, they were spread intentionally to watercourses throughout the UK and also soon spread quickly into the wild throughout watercourses and can even cross land to infect new water courses.

crayfish features

Small lobster like freshwater crustacean, they grow up to 16cm long. Their main identifying features are a turquoise/white blotch on the hinge of the claw and bright red colouration to the underside of the claws.

Not to be confused with:

Native white clawed crayfish, the only native UK crayfish, is much smaller growing only up to 10cm and the underside of the claws are a dirty white/pink colour. The cervical groove (line between head and body) has spikes whereas the same groove on signal crayfish is smooth.


Biodiversity: The signal crayfish carry a fungal disease (crayfish plague) which is lethal to the endangered native white clawed crayfish in England, Wales and Ireland.   They also feed on a range of aquatic invertebrates and fish eggs and compete for habitat directly affecting native fish populations.

Amenity: Their burrowing tendencies cause the undermining of river banks and increase erosion.