A popular tourist destination in Cornwall has been inundated by a stampede of poisonous spider crabs.
Footage shared on social media captured the teeming crustaceans massing in the shallows of Porthgwidden Beach, St Ives.
The crabs are there to shed their shells before returning to their breeding grounds as part of the species’ annual migration pattern to seek warmer waters.
When crabs molt, they come out the back of their shell, leaving behind the entire exoskeleton, including the legs and eye stalks, which may look like a crab intact.
A scuba diver who dived to catch a glimpse of the spectacle said she had never seen spider crabs accumulating in such large numbers.
Kate Lowe, a marine photographer who snorkels in Porthgwidden all year round, said: “I snorkel most days all year round, but I don’t I’ve never seen spider crabs in such numbers.
“When we got to the beach, it looked like there were a lot of dark rocks under the surface. But it turned out there were thousands of crabs just two or three steps into the water. .
She added: “It was really amazing. They were only knee high. I was able to float in the water on top of them and tried not to step on them.
“A lot of tourists were screaming at the sight of them.”
Mass gathering is thought to help crabs protect themselves from predators while they wait for their new exoskeletons to thicken and harden.
Crustaceans have a venomous bite that can kill their predators, but is harmless to humans.
Despite the reported boom in spider crab numbers in UK waters, there is little market in the UK for spider crab meat, despite it being considered a delicacy in European countries, including Spain and France.
But National Coastwatch St Ives told Cornwall Live: ‘It’s just crab shells, they’re not dead.
“They throw shells for new ones.”
Last July, a congregation of spider crab carcasses washed up on the beaches of Anglesey in North Wales.
Photographs similar to those in Cornwall today captured the gruesome picture where the legs, claws and shells of beached spider crabs had gathered.