Invasive Chinese mitten crabs are spreading across the United Kingdom and devastating ecosystems.
Now, conservation officials have installed a new trap in hopes of curbing the prolific creatures. They’re also asking members of the public to report sightings of the crafty crustaceans online to help researchers track their distribution.
Scientists installed the new trap in Pode Hole, a small town at the intersection of several drainage channels in eastern England about 120 miles north of London. They hope to catch the crabs as they make their way downstream toward the North Sea to reproduce.
They also plan to freeze and dissect some of the captured crustaceans so they can learn more about what the crabs have been eating.
“[The trap is] like an extended letterbox that goes across the weir [a low dam], with two openings, one facing upstream and one downstream,” says Paul Clark, a marine biologist at the Natural History Museum in London who’s working on the trap project, to the Guardian’s Donna Ferguson.
If the inaugural trap proves successful, scientists hope to eventually install them elsewhere around the country. This first trap is a collaboration between the Natural History Museum, the Lincolnshire Wildlife Trust and the Welland and Deepings Internal Drainage Board.
The crabs are not a new problem, having first arrived in the country around 1935. But the invasive population is growing in number and extending its range to new waterways within the UK. They now inhabit the Humber, Tyneside, Dee and Severn rivers, as well as many other waterways.
Native to East Asia, the creatures have spread to Europe and North America within the last century. They’re named for the hairy bristles covering their two, white-tipped claws, which make it look like the crab is wearing mittens. The crabs are typically brown or greenish in color and have eight long, pointy walking legs. Their shells are typically three to four inches wide but, factoring in their legs, they can grow to the size of a “ten-inch dinner plate,” writes Sky News’ Megan Harwood-Baynes.
The crabs are problematic for several reasons. They dig burrows, which can contribute to stream bank erosion and weaken levees. They also use their sharp claws to damage fishing gear, and they’ve been known to steal fishers’ bait and catch.
As omnivores, they eat nearly everything, which can disrupt the delicate balance of underwater food webs and ecosystems. They also compete with native species for habitat and food.
"Our biodiversity is being depleted because of them," Clark tells BBC Radio Lincolnshire, as reported by BBC News’ David McKenna.
What’s more, the crabs are prolific reproducers. Adults live in freshwater, but must migrate to saltwater to reproduce. Females can carry between 250,000 and 1 million eggs.
The crabs are a tasty autumnal snack in China, where some clever entrepreneurs have even figured out how to keep them fresh in vending machines. However, in the UK and the United States, it is illegal to import, export, sell, acquire or purchase live Chinese mitten crabs without a permit.
But those laws haven’t stopped smugglers: In recent years, U.S. law enforcement authorities have cracked down on illegal Chinese mitten crab imports via an operation codenamed “Hidden Mitten,” as Rene Ebersole reported for National Geographic in 2020.