Rob Jordan / 2020VISION / Signal crayfish (Pacifastacus leniusculus) in a defensive posture after being caught by The Tweed Foundation monitoring the species population and spread on the River Till, Northumberland, England, UK...

Rob Jordan / 2020VISION / Signal crayfish (Pacifastacus leniusculus) in a defensive posture after being caught by The Tweed Foundation monitoring the species population and spread on the River Till, Northumberland, England, UK...

Rob Jordan / 2020VISION / View of the River Till, part of area where The Tweed Foundation are monitoring the population and spread of Signal Crayfish (Pacifastacus leniusculus), Northumberland, England, UK, October

Michel Roggo / Signal crayfish (Pacifastacus leniusculus) Europe, introduced from North America

Paul Hobson / Signal Crayfish {Pacifastacus leniusculus} Leicestershire, UK

Andy Sands / Signal Crayfish (Pacifastacus leniusculus) defence posture in chalk stream, Hertfordshire, UK

Alex Hyde / Signal Crayfish (Pacifastacus leniusculus), a species introduced to the UK from North America. They are far larger and more aggressive than the native species, and can easily out-compete them. Photog...

Linda Pitkin / 2020VISION / Signal Crayfish (Pacifastacus leniusculus) on lake bottom, Wraysbury Lake, Middlesex, England, May

Linda Pitkin / 2020VISION / Signal Crayfish (Pacifastacus leniusculus) on lake bottom, Wraysbury Lake, Middlesex, England, May

Rob Jordan / 2020VISION / Signal Crayfish (Pacifastacus leniusculus) placed on a population spread monitoring map, River Till, Northumberland, England, UK, October

Rob Jordan / 2020VISION / Signal crayfish (Pacifastacus leniusculus) being held by 2020VISION Young Champion Shaun Robertson working as a field assistant for The Tweed Foundation monitoring the species population and spread, R...

Rob Jordan / 2020VISION / 2020VISION Young Champion Shaun Robertson hauling in humane traps used to catch Signal Crayfish (Pacifastacus leniusculus) for The Tweed Foundation to monitor the species population and spread, River...

Rob Jordan / 2020VISION / Signal crayfish (Pacifastacus leniusculus) being held by 2020VISION Young Champion Shaun Robertson working as a field assistant for The Tweed Foundation monitoring the species population and spread, R...

Rob Jordan / 2020VISION / Signal crayfish (Pacifastacus leniusculus) being measured by 2020VISION Young Champion Shaun Robertson working as a field assistant for The Tweed Foundation monitoring the species population and sprea...

Rob Jordan / 2020VISION / Signal crayfish (Pacifastacus leniusculus) in a defensive posture after being caught by The Tweed Foundation monitoring the species population and spread, with the River Till in the background, Northu...

Rob Jordan / 2020VISION / Signal crayfish (Pacifastacus leniusculus) in a defensive posture after being caught by The Tweed Foundation monitoring the species population and spread on the River Till, Northumberland, England, UK...

Rob Jordan / 2020VISION / Signal crayfish (Pacifastacus leniusculus) being held by 2020VISION Young Champion Shaun Robertson working as a field assistant for The Tweed Foundation monitoring the species population and spread, R...

Rob Jordan / 2020VISION / Signal crayfish (Pacifastacus leniusculus) being measured by 2020VISION Young Champion Shaun Robertson working as a field assistant for The Tweed Foundation monitoring the species population and sprea...

Rob Jordan / 2020VISION / Signal crayfish (Pacifastacus leniusculus) being held by 2020VISION Young Champion Shaun Robertson working as a field assistant for The Tweed Foundation monitoring the species population and spread, R...

Niall Benvie / 2020VISION / Signal crayfish (Pacifastacus lenisculus), an introduced species, Scotland, UK, August meetyourneighbours.net project

Paul Hobson / Signal crayfish {Pacifastacus lenuisculus} American species now living wild in UK.

WILLIAM OSBORN / Signal crayfish male captive {Pacifastacus lenuisculus} from N America