A type of stinging jellyfish has been spotted in the “hundreds of thousands” in Bermuda’s waters this year, a marine biologist has warned.

Choy Aming posted on Facebook that he had seen pelagia noctiluca offshore and inshore.

The Department of Environment and Natural Resources advised swimmers to keep their distance and avoid touching the animals even when they are washed ashore as their stinging cells can remain active.

Mr Aming wrote: “Just a heads up. This is pelagia noctiluca aka the warty jellyfish aka the mauve stinger.

“We get some every spring but this year there are literally millions of them. North and South Shore have some but there are giant lines of hundreds of thousands offshore.

“This is likely an unusual event but with warming seas we can expect jellyfish numbers to increase significantly in the future. They do sting but not as bad as a man o’ war.”

Mr Aming added in the post: “I have had lots of people contact me about them. There are even a few in Flatts Inlet.

“Vinegar is probably the best antidote if you get stung but I realise most people are not in the water yet.”

He noted that using urine on the sting was not the best remedy.

A spokesman for the DENR said: “The warty jellyfish, pelagia noctiluca, appears every spring as the surface oceans warm.

“If the conditions for reproduction are favourable, you can have a bloom with millions of them.

“The winds and tides can aggregate or disperse them, with some found along the North and South shores.

“It is unsurprising to hear of long lines of hundreds of thousands offshore. The surface water flow pushes them into the lines, just as we see with Sargassum.”

He added: “Swimmers are advised to keep their distance as the tentacles can be unpredictably long.

“Also, do not pick up jellyfish left on the beach. Like the Portuguese man o’ war, stinging cells can remain active many hours after being left on the tide line.

“If you get stung, the recommended treatment is to dab the sting with vinegar or hot — not scalding — water.

“Remember that depending on the individual's reaction, a single or multiple stings can trigger an allergic reaction, which may require a visit to the emergency room.

“If stung, monitor for an allergic reaction and, if necessary, seek appropriate medical care.”

According to the Scripps Institution of Oceanography, pelagia noctiluca has eight tentacles and four long oral arms, which are used to move captured prey to the animal’s mouth.

Its colour varies from purple to yellow and it often has warts that contain stinging nematocysts on the bell surface.

The Smithsonian National Museum of Natural History website said the mauve stinger’s name in German means night light, referring to the jelly’s reddish colouring and its bioluminescence.

It reported: “Unlike a night light, however, this jellyfish can become startled and leave a trail of glowing mucus behind.”

There was also a sighting of large numbers of by-the-wind sailors, also known as velella, a type of jellyfish that is harmless to humans.

Laura Rego posted a photograph on Facebook on Monday that showed them in abundance at Flatts Inlet.

She told The Royal Gazette: “I was enjoying an afternoon with my children at the aquarium and my son spotted them.

“I was just so surprised by so many of them. I’ve never seen them before.”

Jelly Watch, a website recording sightings of jellyfish and other marine organisms, reported: “Velella are not dangerous to humans.

“They can sting and capture small prey, but they also harbour algal symbionts, giving mature specimens a greenish or even brown tint.”