Pacifastacus leniusculus
Pacifastacus leniusculus
Originally introduced to the UK in the late 1970s and 1980s as a potential food source, the American Signal crayfish has since spread rapidly across rivers and streams in England, posing a serious threat to native wildlife.
They can grow up to 16cm long (from tail to top of head).
They usually have a turquoise/ white blotch on the hinge of the claw and the underside of their claws are bright red.
It is a criminal offence to release or allow to escape into the wild signal and other non-native crayfish species without a licence (Source: EA)
Signal crayfish are more than just unwelcome guests—they’re aggressive invaders that:
Even a single crayfish can carry the plague. Although harmless to humans, plague spores can cling to damp clothing, boots, and equipment—spreading the disease to new, uninfected areas.
Protecting our native White-clawed crayfish starts with simple actions:
After spending time in or near rivers:
Handling crayfish—whether native or invasive—requires a special licence.
Unlicensed trapping can harm native populations and disrupt conservation efforts.
Seen a Signal crayfish? Help track their spread:
