This 20 kg beast of a jellyfish was spot by a wildlife expert while he was out swimming with his pet dog. Matt Slater, a Wildlife Trust Officer, managed to catch the creature on film in the Percuil Estuary near St Mawes, Cornwall.

Increased sightings of these ‘barrel’ jellyfish have been made in the area and is being blamed on the number of long, sunny days which have increased sea water temperatures.

Luckily for Mr Slater and other bathers the jellyfish’s sting are too weak to penetrate human skin.

Mr Slater said: ‘It was an otherworldly experience. These creatures are incredibly beautiful when you get close to them.’ The jellyfish have a type of mucus on the outside of their tentacles to catch plankton – their only source of food. They swim searching for large patches of plankton.

The Marine Conservation Society reported other sightings along the south and west costs of England.

Mr Slater said: ‘In the spring tiny anemone polyps living on the sea bed expand in size and bud off thousands of larvae. Most years these larvae will perish but when the weather is warm there is plenty of planktonic food and predators do not eat them all, large numbers of them survive creating huge jellyfish swarms.’

Pic: BBC