Large numbers of “alien-looking” blue creatures have been reported washing up on Cornwall’s beaches over the last few weeks.

At first glance they resemble an oval jellyfish and are a deep, vivid blue colour, with concentric circles like a fingerprint and a fin-like ‘sail’.

Now the Cornwall Wildlife Trust has explained they are known by the scientific name Velella velella, or the more common name, ‘by-the-wind-sailor’.

The creatures are hydrozoans – a colony of tiny individual animals called hydroids. They are similar to the Portuguese man o’ war, rather than jellyfish. Fortunately, the stings are not powerful enough to harm humans or dogs.

There have been reports made via the charity’s Facebook page of large numbers at many of Cornwall’s popular beaches including: Newquay’s Fistral beach, Lansallos beach, Harlyn Bay, Port Gaverne, Port Quin, Mawgan Porth, Porthtowan, Perranporth, Polly Joke, Trevellas Cove, Gwithian, Portreath – where one person said there were “zillions the other day” – as well as “millions” at Praa Sands, and at Crantock, where a member of the public noticed that their dog’s paws didn’t get stung as they ran over them.

Some of the creatures were no bigger than a 50p coin, while others were more substantial, up to 10cm long.

Video: Abby Crosby / Cornwall Wildlife Trust

Matt Slater, marine conservation officer at Cornwall Wildlife Trust, has now explained what Velella velella actually are, saying: “These creatures are hydrozoans – a colony of tiny individual animals called hydroids.

“They float on ocean currents, and the sail on top allows them to catch the wind like a sailing boat and travel long distances effortlessly, using their stinging tentacles to catch small marine organisms as they go.

“The colony are connected by canals that enable the individuals to share the food.

“Fortunately, the stings are not powerful enough to harm humans or dogs, although it is not advisable to touch them and then touch your face and eyes, as they may cause skin irritation.

“Dogs love eating them – they have a strong smell of the ocean – but I don’t think they are good for them.”

Falmouth Packet: People have reported the creatures in their 'zillions'People have reported the creatures in their 'zillions' (Image: Abby Crosby / Cornwall Wildlife Trust)

As to why they have appeared on Cornwall’s beaches in such numbers this month, Matt added: “As their common name suggests, by-the-wind-sailor are at the mercy of the prevailing winds.

“They live their entire lives in the open ocean, and it’s bad news for them if they ever meet land.

“If there are extended periods of onshore breezes, they can be blown ashore from further out to sea. We have had really strong north and north-west winds for well over a week, which is probably why they have been coming ashore in such numbers.

“Sadly, once they are onshore they die, and it’s futile trying to save them if the winds are onshore. However, new floating colonies will already be forming out in the ocean.”