- Oops!Something went wrong.Please try again later.
Photographs show legs, claws and carapaces of washed-up spider crabs in various states of dismemberment and decay.
However, beachgoers have been reassured that the apparent mass die-off is not as it seems.
Each year the species not only migrates to warmer waters, and then returns again to their breeding grounds, but also moult, shedding their spiny exoskeletons, including their legs, claws and even their eye-stalks, and emerge even bigger than before.
The grisly scene on the shore, in which many of the crabs appear to be completely whole, is merely the result of the crabs’ natural moulting process – similar to how snakes shed their skin.
When the crabs moult, they emerge from the back of their shells and are temporarily soft-bodied and therefore vulnerable to predators.
Despite this explanation, there remain concerns that the worsening climate crisis is warming UK waters enough to see a considerable proliferation of spider crabs around the coast.
Watch: Thousands of spider crabs mass off Cornish coast in rare natural phenomenon
Tim Harris, who visited Traeth Mawr beach on Anglesey last week reported the phenomenon to Natural Resources Wales, and said: "It’s no exaggeration to say there are thousands and thousands washed up.”
Richard Lee, who photographed the piles of crabs, described it as a "really strange phenomenon", adding that there were "thousands and thousands" of them.
During this point in their lifecycle they become highly gregarious – as there is safety in numbers – and they congregate near the seashore in a further effort to avoid predators.
Despite the reported boom in numbers of spider crabs in British waters, there is little market in Britain for spider crab meat, despite it being considered a delicacy in European countries including Spain and France.
Furthermore, the crabs which are landed in Britain are now more difficult to export to European markets due to Brexit.
Before Brexit, around 85 per cent of spider crabs caught off the Cornish coast were exported to Spain, but new red tape due to the vote to leave the EU means extra paperwork and border checks.
Last year fisheries in the UK debated "rebranding" spider crabs as "Cornish king crabs" to appeal to UK diners.
As well as the rise in spider crab numbers and the simultaneous collapse in demand, fishermen are further aggravated by the presence of the crabs, with fishermen in Hastings telling The Independent the creatures’ sharp spiny carapaces cause significant amounts of damage to their nets.