Thousands of poisonous crabs swarm St Ives beaches in Cornwall

Thousands of poisonous crabs have swarmed the beaches of Cornwall, shedding their shells before returning to the depths of the sea.

The carpet of crabs that gathered in the shallow waters of St Ives is a sight that is becoming increasingly common in the summer due to rising sea temperatures.

Spider crabs are instantly recognisable for their long legs and pincer claws and have a venomous bite that is poisonous to their prey but harmless to humans.

While their presence at Porthgwidden Beach was enough to put many bathers off entering the sea, some did take the chance to snorkel above the mass of crustaceans to view the hair-raising spectacle.

Once the crabs shed their shells, they return to depths of 300ft, leaving the water clear for those hoping to paddle in the waters.

Kate Lowe, a marine photographer, captured the event in the same week a woman snorkeller was bitten by a blue shark further around the Cornish coast, off Penzance.

Kate said: "I go snorkelling most of the time throughout the year, but I have never seen spider crabs in such numbers.

"When we turned up at the beach, it looked as though there were lots of dark rocks under the surface.

"But it turned out that there were thousands of crabs just two or three steps into the water.

"It was just really incredible, they were only knee-deep. I was able to float on the water above them and tried not to step on them.

"A lot of the tourists were squealing at the sight of them.

"Their shells were just floating around."

Spider crabs - Hyas araneus in Latin - usually gather in huge numbers in shallow water to protect themselves from predators.