Stock Photo - Named after the colouration on the underside of its claws the white clawed crayfish Austropotamobius pallipes is now considered an endangered species within the UK There has been human impact due to pollution and habitat disturbance however the main problem lies with competition from an alien species Commercial introduction of the larger signal crayfish Pacifasticus leniusculus from the U S in the 1970s led to physical displacement of the native species and the spread of a fungal disease commonly referred to as the crayfish plague To 120 mm UK and Ireland, Spain to Croatia IUCN Red List Vulnerable 2009