'Invasion' of spider crabs shocks locals as they smother ocean floor

These relatively large, orange creatures have been observed scuttling along the shallow ocean floor of the state's Eyre Peninsula.

An Oyster farmer from the region Lester Marshall shared with the media his shock at the sheer amount of crabs in the state's waters this winter.

"For all the years I've been oyster farming here, I've never seen this many," Mr Marshall said.

"We've had a big invasion of Spider Crabs turn up in mass numbers and they've marched up the channels in Coffin Bay ... they've come right across into Kellidie Bay."

Spider crabs are distinguishable from other crabs by their elongated and slender legs, which inspired their name.

These unique creatures can grow up to 18 centimetres in width, while their claws and legs can extend to as long as 70 centimetres.

The Victorian Fishing Authority states on its website that it's common for spider crabs to assemble in large groups each winter.

It said the behaviour is driven by their need to find safety in numbers during moulting, a time when their soft shells make them more vulnerable to predators.