Experts are warning Brits to kill this river-dwelling creature on sight – but there are a few things you should know before you encounter one.
The American signal crayfish was brought to our shores in fish farms back in the 1970s. Many of the creatures escaped and it quickly became an invasive species. The animals carry a crayfish plague that can infect and kill native river species, and they also feast on local, smaller crayfish varieties.
The unsightly critter also destroys local crayfish habitats and beats them to other food. Not only that, but it burrows into riverbanks, weakening the waterway and making flooding more likely. The crayfish is such a problem, it is now illegal not to kill one if you spot it.
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However, destroying an American signal crayfish is no mean feat – you must crush its brain in order for it to die. And before you go out crayfish-hunting, you should also make sure you can tell the difference between the American variety and its native counterpart, the European white-claw crayfish.
Sadly, a staggering 90% of the latter’s population has now disappeared, so it’s vital you leave them unscathed if you spot them. But how can you tell the difference?
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Dr Emily Smith of The Angling Trust – the national governing body and representative organisation for all freshwater and sea anglers in England – explained the difference in a YouTube video.
Firstly, you’ll want to check the creature’s claws. The undersides of American signal crayfish’s claws are red, while they have whiteish hinges at the claws which is more obvious in larger animals. “If you’re identifying those features you can start to narrow in and feel more confident about what you’re looking at,” she said.
The American species also have two small bumps on the back of its head. The second one “might be a lot smaller,” according to Dr Smith. Towards the body, the two types of crayfish have different body textures, too.
“Look at the the kind of texture of the species – so for a signal crayfish it’ll be completely smooth, for a white claw crayfish it will have more ridges and some kind of uneven texture,” she added.
If you do come into contact with an American signal crayfish, it’s vital to wash your shoes and clean any boats or fishing equipment before you go home.