Mysterious 'green alien' on North Wales beach that can eat victims three times its own body length
Covered in bristles, making it appear furry, the half foot-long creature was found by dog walker Simon Parker on Pensarn Beach, Conwy. Not knowing what it was, and seeing its fringe flash green, he used Google Lens to identify it as a Sea Mouse.
'I found it at the water's edge just after low tide," he said. "Unfortunately, it didn't appear to be alive. The Sea Mouse was approximately five or six inches long with brightly coloured bristles down the sides.'
Sea Mice are not uncommon but they are rarely seen, occasionally washing up on beaches in rough weather, or stranded by very low tides. By coincidence, another sandy fur-ball was found in March on Oxwich beach, Swansea.
The stunned reaction to seeing one at Pensarn would not have surprised the Wildlife Trusts, which said the Sea Mouse is 'unlike anything else in the sea'. Although it can grow to 20cm long and 6cm wide, it's actually a marine worm.
Despite its habit of lying buried head-first in the sand, it's a critter with a very special skillset. Its spines usually have a deep red sheen, warning off predators. But when light shines on them, they flash blue, green and gold, giving the worm a shimmering, iridescent fringe.
It's a phenomenon called pseudo-birefringence, the only known example of 'photonic engineering' in nature. As the spines process light with almost 100% efficiency – needed in the sea's murky depths – some researchers believe this talent may give way to new communication technologies.
If you ever find one, you can see its fibre-optic opulence for yourself. Pop it in a vessel of seawater and the magic will appear: a groovy, psychedelic display completely at odds with its slightly creepy appearance.
Why is a worm called a mouse? It's thought the name stems from looking like a bedraggled mouse when washed up on shore.
Its Latin name, Aphrodita aculeata, is just as bizarre. While aculeata means 'spiny', the genus name refers to Aphrodite, the ancient Greek goddess of love – apparently because the worms resemble women's genitalia.
The Sea Mouse is an active predator of small crabs. It also preys on other worms, able to eat victims more than three times its own body length.
Occasionally they are spotted wriggling across the sand, invariably an unnerving sight for beachgoers. They are not generally harmful to people, though their sharp bristles that can cause irritation if they puncture the skin.
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