Massive gatherings of spider crabs ‘are not dangerous to humans’

spider crabs

Conservationists are urging visitors to Cornwall to enjoy the sight of massive gatherings of spider crabs in a bid to counter claims the crustaceans are ‘venomous’.

In recent weeks, hundreds of crabs have congregated in knee-deep water in popular tourist spots such as Newquay, St Ives, Falmouth and St Austell.

The natural phenomenon, in which crabs band together for protection while shedding their shells to grow a new exoskeleton, was only spotted once in the UK last year on Falmouth beach.

Spider crabs are most populous in the warmer waters of the Mediterranean Sea, but their numbers have increased in UK waters in recent years.

Marine biologists believe the boom is a direct result of climate change and warming sea temperatures.

The crabs may look like giant spiders, but the Cornwall Wildlife Trust has stressed that they are not dangerous and have moved to correct media reports that they are poisonous.

spider crabs
Giant spider crabs have massed in several places off the Cornwall coast this summer (Katie Maggs/PA)

Matt Slater, head of marine conservation at the trust, said: “I’ve spent my entire career trying to get people to appreciate incredible sea animals like spider crabs.

“Reports that they are poisonous are simply false and could damage their reputation. These animals are truly unique and completely harmless to humans.

He continued: “Please get out, enjoy our coastline responsibly and see these sensational displays of spider crabs if you are lucky enough to see one.”

During moulting, crabs seek safety in numbers from predators while they wait for their new shell to harden and travel to shallow coastal waters as the process is an integral part of their life cycle.

The Cornwall Wildlife Trust is now asking the public to register any spider crab sightings with them, including any mass gatherings, to help them identify patterns in their behavior and migrations.

Mr Slater said: “We hope these massive sightings are a sign that spider crab populations are healthy. We would love to hear of other gatherings taking place around the Cornwall coastline.

“Our seas are full of surprises and there is still so much we don’t know about them.”

Katie Maggs, a volunteer with Cornish conservation society Mounts Bay Marine Group, filmed one of the gatherings.

She said: ‘The massive spider crab molt looked like something you’d see in a tropical country, but it’s happening here in Cornwall! I feel so lucky to have witnessed this first hand.

About Marco C. Nichols

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