If you go down to the beach today… be careful not to step on a potentially-deadly jellyfish

Look, but don't touch — large numbers of colourful Portuguese man o' wars have been stranded on the UK coastline.

Autumn beach walkers are warned to watch out for Portuguese man o’ war, who have recently been spotted in high numbers on the shoreline in the south west.

The jellyfish-like creatures are in fact floating colonies of hydrozoans, a group of tiny marine creatures living together and behaving as one animal.

More than 60 man o’ wars were spotted on a beach in Cornwall on Monday as persistent south westerly winds blow the hydrozoans away from their typical open ocean setting.

Packing a punch: Tendrils can extend 165 feet in length. Credit: Alamy Stock Photo

‘The tentacles deliver a powerful sting, which is very painful and sometimes deadly, so walkers and their pets give them a wide berth.

‘It’s the tentacle-like polyps that can give an agonising and potentially lethal sting,’ said Marine Conservation Society (MCS) jellyfish expert Dr Peter Richardson.

‘Because a stranded Portuguese man o’ war looks a bit like a deflating purple balloon with blue ribbons attached, children may find it fascinating.

Man o’ wars feature a distinctive purple-tinged float. Credit: Alamy Stock Photo

‘It’s well worth making sure you know what these animals look like and that no one picks them up.’

The MCS is urging the public to report any sightings of Portuguese man o’ war to its website so they can get a better idea of the extent of the strandings.

Recent reports show the creatures washing up in Cornwall, Devon, and Wales in the past few weeks. The last time there was a major stranding event was when hundreds of thousands washed up in the south west in 2017.

Remarkable creatures

Man o’ wars have a distinctive purple-tinged float that is visible on the water’s surface. The crest of the float is tipped with pink and is sometimes caught in mats of seaweed.

The creatures can deflate their float and submerge themselves to avoid threats on the surface.

Tentacle-like ‘fishing polyps’ hang below the surface of the water.  The long, thin tendrils can extend 165 feet in length, although 30 feet is more the average.

Man o’ wars lose their colour quickly after being stranded on beaches and can appear translucent with just a tinge of purple.