Beachgoers are being encouraged to look out for large groups of spider crabs along Cornwall’s coastline during the summer holidays amid increasing reports of mass gatherings filmed just metres away from the shore.

The crustaceans have been spotted carpeting the ocean floor at multiple popular tourist destinations in recent weeks.

The spider crab aggregations – or gatherings – used to be rare to see in UK waters, but Cornwall Wildlife Trust’s marine experts have described this summer as being “unusually spectacular” for sightings.

This year, the crabs have been seen rallying together by divers and snorkellers across the Duchy in Newquay, St Ives, Falmouth, St Austell Bay and on the Lizard Peninsula.

Spider crabs are known to resemble the arachnids they are named after. Their long, spiny legs and claws spanning up to one metre give them their spider-like look.

Each summer, these distinctive creatures travel from deep to shallow coastal waters as part of their life cycle. They congregate in huge numbers and shed their old shells in a synchronised act; protecting themselves from predators while they wait for their new exoskeletons to harden.

The spider crab mass moulting looks like something you’d see in a tropical country, yet it’s happening right here in Cornwall! 

Photo: Matt Slater

Information: Cornwall Wildlife Trust