A beach walker came across a jellyfish with a powerful sting warning others to watch out for the potential threat.
Richard Lee has issued a warning after finding several Lion's mane jellyfish on a popular beach in Anglesey, Wales.
The sting of a Lion's is rarely fatal - but it may cause skin problems which feel like a bad nettle rash.
North Wales Wildlife Trust (NWWT) recommends people go to the doctor if their symptoms become severe.
The marine animal has "all the beauty and bite of a lion", it adds, according to North Wales Live.
The jellyfish gets its name from its red-orange cluster of tentacles that can reach enormous lengths.
It is often cited as the world’s longest animal, with one found off the coast of Massachusetts, USA, having tentacles measuring 36.6metres (120ft) long.
Mr Lee, a holidaymaker from Lincolnshire, said the ones he saw on Lligwy beach, near Moelfre, were much smaller as is typical in the Irish Sea.
Measuring about 1.5ft across, it was less than a quarter of the size of record-breaking specimens.
He said: “I came across this bad boy on my last day on the island. There were a few others on the beach.
"As the summer school break has just started, I thought visitors should be warned before some poor kid gets hurt.”
Lion’s manes are usually found in waters to the north of Scotland, although there have been sightings around the North Wales coast.
In 2016, endurance athlete Liane Llewellyn-Hickling was forced to abandon an attempt to become the first woman to swim around Anglesey in one go after she was stung more than five times by a Lion’s mane jellyfish.
Their tentacles are packed with stinging cells that are used to catch fish and smaller jellyfish.
On its website, NWWT warned: “Fragments of its tentacles will sting you even if they’re no longer attached to the jellyfish.
"They will still sting long after they’ve been on the shore.”
The jellyfish was featured in a Sherlock Holmes short story as the killer of a professor who died while swimming.
In healthy people, however, their stings are not known to be fatal unless they suffer from certain allergies.
Four years ago, a mum claimed her son was badly stung by a Lion’s mane when jumping into the sea near the Great Orme, Llandudno.
When he surfaced, his top half was said to have been covered in an “orange-ish blob”.
He subsequently suffered weals that spread across his back, shoulder and side of face.
“He was in agony for about eight hours,” she said. “I mean, he was an absolute mess.”
On that occasion, doctors advised antihistamines and pain relief with warm and cool baths.
Some studies show vinegar can deactivate jellyfish stings but to nullify the venom, water of 45 degrees or more should be applied.
NWWT advises: “Lion’s mane jellyfish give a very nasty sting, so consult a doctor if swelling or weals are severe.
“In the meantime, scrape the area with a clean stick or remove the tentacle with tweezers if you have them to hand, then rinse the area with warm to hot water to reduce swelling.”
In 2010, some 150 beachgoers were stung by Lion’s mane remains in New Hampshire, USA. Given their considerable size, it is possible that all 150 were stung by a single jellyfish.
They can grow to be longer than Blue Whales, the world’s largest mammal.
However Lion’s manes have a rival for the title of world’s longest animal.
In 1864, a bootlace worm was found washed up on the coast near St Andrews, Scotland, that measured 55metres (180ft) long.
The finding has since been disputed: while bootlace worms can grow to over 30metres, they can also stretch to several times their natural length.
