The signal crayfish (Pacifastacus leniusculus) is an invasive freshwater species in the UK, introduced in the 1970s for aquaculture. Native to North America, it has spread widely across UK waterways, outcompeting the native white-clawed crayfish (Austropotamobius pallipes) and contributing to its decline. Signal crayfish are highly adaptable and aggressive, with burrowing behavior that erodes riverbanks and disrupts habitats. They are also carriers of crayfish plague (Aphanomyces astaci), which is lethal to native crayfish.
