Photos shared on social media captured the swarms of crustaceans gathering in the shallows off 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 emerge from the back of their shell, leaving behind the entire exoskeleton, including legs and eye stalks, which may resemble an intact crab. A snorkeler who dived to see the sight said he had never seen spider crabs congregate in such numbers. Kate Lowe, a marine photographer who snorkels at Porthgwidden all year round, said: “I go snorkelling most times of the year but 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.” He added: “It was really incredible. It was only up to the knees. I was able to float in the water above them and tried not to step on them. “Many of the tourists were screaming at the sight of them.” It is believed that the mass gathering helps the 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 a reported boom in the number of spider crabs in British 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: “They’re just the shells of a crab, they’re not dead. “They cast shells for new ones.” Last July, a community of spider crab carcasses washed up on the beaches of Anglesey off north Wales. Photographs similar to those from Cornwall today captured the gruesome tableau where the legs, claws and shells of washed-up spider crabs had gathered.
