The UK’s rivers and ecosystems are facing a serious threat from a small but highly destructive invader: the American signal crayfish. This aggressive crustacean is wreaking havoc on native species, riverbanks, and waterways, and Brits are being urged to kill these creatures on sight if encountered. Here’s everything you need to know about why this invasive species is so damaging, how to identify them, and what you can do to help protect the UK’s aquatic habitats.
You’re allowed to kill these if you see them (NWWT)
The American Signal Crayfish Invasion: A Growing Environmental Threat
The American signal crayfish arrived in the UK in the late 1970s, originally brought over for fish farms. However, these crayfish quickly escaped into local waters, spreading across the UK and outcompeting native crayfish. Their ability to carry and spread a deadly “crayfish plague” without being affected by it has pushed the native white-clawed crayfish to the brink of extinction. In addition, signal crayfish destroy habitats, undermine riverbanks, and endanger local biodiversity.
These invasive crayfish don’t just kill native species through predation—they also damage the environment physically. Their burrowing weakens riverbanks, making them prone to collapse and increasing flood risks in the surrounding areas. This is a classic example of an invasive species throwing the local ecosystem off balance, causing widespread disruption to both flora and fauna.
How to Identify the American Signal Crayfish vs. the Native White-Clawed Crayfish
The first step in tackling this invasive species is to be able to identify it correctly. Confusing the American signal crayfish with the UK’s native white-clawed crayfish could have disastrous consequences, as white-claws are endangered and need all the protection they can get. Here are some key characteristics to help you distinguish between the two:
- American Signal Crayfish: Look for large claws with a red underside and a distinct white or blue blotch near the claw joints. These crayfish can grow up to 12 inches in length, with a bulkier appearance.
- White-Clawed Crayfish: True to its name, the native white-clawed crayfish has claws that are paler in color, usually white or light in appearance. They are generally smaller than their invasive cousins and have a more delicate look.
By carefully examining the claws, you can avoid harming the native species while targeting the destructive American signal crayfish.
Why It’s Important to Kill Signal Crayfish on Sight
It might seem drastic to advocate for killing these crayfish on sight, but it’s necessary to protect the ecosystem. In fact, it’s illegal to release American signal crayfish back into the wild if you catch one. Their population explosion has devastated native species, especially the white-clawed crayfish, with estimates suggesting that 90% of the native population has been lost.
Apart from spreading the crayfish plague, signal crayfish also destroy fish populations by eating fish eggs, young fish, and aquatic vegetation. Their presence disrupts the entire food chain, making them an even greater threat to river ecosystems.
Methods for Humanely Killing American Signal Crayfish
If you encounter an American signal crayfish, here are some recommended methods for humane euthanasia:
- Stab the Brain: This is considered the most humane and effective method. If you’re carrying a knife, stab directly into the crayfish’s head to destroy the brain.
- Crush Under a Rock: Not everyone carries a knife, so using a rock to quickly crush the crayfish is an alternative. It might sound unpleasant, but this method is swift and prevents the crayfish from spreading further.
Remember to be certain of the species before taking action, as harming native white-clawed crayfish is illegal.
The crays… They’re an invasive species (Getty Images Stock)
Preventing the Spread of Signal Crayfish
Beyond killing individual crayfish, there are other ways to prevent the spread of signal crayfish. One essential step is to ensure that you do not transfer any aquatic materials or moisture between rivers, lakes, or streams, as this can inadvertently spread the plague they carry. Here’s how you can help contain the problem:
- Clean Your Gear: If you’ve been near water where signal crayfish are present, make sure to thoroughly clean and dry any boots, fishing equipment, or boats before moving to another location.
- Dry Your Dogs: If you’ve brought your dog along to a river, dry them off well to prevent transferring any waterborne pathogens.
- Avoid DIY Crayfish Farming: As tempting as it may be to cook and eat these crayfish, this can create an even greater risk of spreading them. Catching and killing crayfish might help reduce the population, but it’s important not to encourage their presence by creating a food source.
Taking these precautions can help curb the spread of signal crayfish, preventing them from reaching more rivers and harming more local wildlife.
Why the American Signal Crayfish is a “Zombie” of UK Rivers
The American signal crayfish has gained something of a “zombie” reputation, as it appears unstoppable and deadly to the UK’s native aquatic life. Much like a fictional apocalypse, this invasive species devours resources, kills indiscriminately, and spreads an infectious plague, all while threatening the survival of local species. Given the environmental damage they cause, these crayfish need to be “killed on sight” to protect the UK’s rivers.
With no natural predators in the UK, signal crayfish populations have exploded, leaving native species defenseless. This environmental imbalance highlights the importance of vigilance and active measures from the public, as every sighting counts in the fight to contain this invasive species.
Conclusion: Protecting the UK’s Rivers from Signal Crayfish
The invasion of the American signal crayfish poses a severe threat to the UK’s natural habitats, pushing native species toward extinction and degrading riverbanks with their relentless burrowing. Identifying and humanely killing these crayfish on sight can make a tangible difference in slowing their spread and safeguarding the ecosystem.
As Brits, it’s up to us to protect the UK’s rivers and waterways, so the next time you encounter an American signal crayfish, you’ll know just what to do. By being vigilant, spreading awareness, and taking action where possible, we can work together to reduce the impact of these invasive “zombies” on our precious aquatic environments.
