Signal Crayfish - Pacifastacus leniusculus

Alternative names
American Signal Crayfish

Introduced from the USA, these crayfish are up to 15 cm, encased in a tough shell and armed with two large smooth claws. They are bluish-brown to reddish-brown in colour. They have a white to pale blue-green patch near the claw hinge. The claws are orange/red on the underside.

Similar Species

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Identification difficulty

Rivers, lakes and ponds.

When to see it

All year round.

Life History

A voracious predator it will eat almost anything it finds including plants, invertebrates, snails, small fish and fish eggs. It is also a cannibal that makes a meal of its own young. The Signal Crayfish digs burrows up to three feet long in river banks where each year it lays more than 250 eggs at a time. The spread of this species is threatening the future of our native White-clawed Crayfish.

UK Status

This invasive crayfish has now reached plague proportions in many parts of Britain and marine biologists have been desperately seeking a way of halting its relentless spread. It is also well established in Leicestershire and Rutland.

VC55 Status

Common in Leicestershire and Rutland.

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Leicestershire & Rutland Map


Yellow squares = NBN records (all known data)
Coloured circles = NatureSpot records: 2020+ | 2015-2019 | pre-2015

UK Map