Thousands of crabs wash up on Anglesey beach in 'phenomenal' sight

Visitors to a beach on Anglesey discovered what looked like thousands of crabs invading the land.

Thousands of crustaceans covered the sandy beach near Aberffraw on the island’s western coast.

On closer inspection, the algae-covered invaders appeared dead and hollowed out.

"I’ve never seen anything like it," said Richard Lee, 59, a lorry driver from Lincolnshire who was making his first trip to the island.

“It was a phenomenal sight. There were literally thousands of them. But there were no seagulls picking at the crabs, which you might expect if they had just died. It took me back a bit.”

The carcases were the shells of spider crabs, which have distinctive spiny shells and long, spindly legs.

Spider crabs migrate from deep to shallower coastal waters every summer to moult their shells, part of their life cycle that enables them to grow.

Massing a few metres from beaches, they congregate in huge numbers to protect themselves from threats.

During the moulting process, when they crack open their exoskeletons, they become vulnerable to predators.

Exiting through the rear of their shell, the crabs leave behind their entire exoskeletons, including the legs and eye stalks. These then wash up on beaches and, for visitors, they look just like intact crabs.

Their appearance on foreshores periodically prompts public reassurances there is nothing to worry about.

Climate change has been blamed for rising numbers of Spider crabs off the Welsh coast. Common in the deep waters of Cardigan Bay, anecdotal reports suggest populations are spreading north as waters warm.

Last year, a large moulting gathering occurred in Porth Trecastell.

Many species of spider crab are found around the world, from the tiny kelp crabs of North America to the Giant Japanese spider crab that can grow to 13 feet.

Those off the Welsh coast are typically European spider crabs or, less commonly, smaller Great spider crabs.

They are harvested in pots, with most destined for Continental markets where their meat is regarded as a delicacy. In the UK there is little demand for this most mysterious species of crab.