My close encounter with the King of the Stingers: He's known as The Rottweiler, but when JOHN HUMPHRYS was attacked by jellyfish it taught him a painful lesson about who really rules the animal kingdom

The sting felt much the same as you'd get from a nettle. A vigorous, young nettle admittedly, but not particularly unpleasant.

And anyway, I rather like stinging nettles. They're great for butterflies, taste really good in soup and the sting goes away pretty quickly. But it wasn't a nettle that had stung me. It was a jellyfish.

I was swimming off the coast of the Llyn Peninsula in north Wales — one of those countless bits of Britain that are so lovely you have to wonder why we are all apparently desperate to go abroad for holidays.

My assailant was rather lovely, too. It was a compass jellyfish: about six inches in diameter, translucent, with dark orange lines radiating out from the centre of its bell. Less easy to spot were the tentacles stretching beneath it. They got me on my wrist, which turned red and throbbed for a while. But no big deal. The second time was a different story.

The next day I was swimming in the same area (not very sensible with the benefit of hindsight) and brushed against the tentacles of another compass. A bit bigger than the first, but the same reaction. My wrist swelled a little, but the pain was no worse than the first sting. No harm done. Or so I thought.

It was when we were having breakfast about half an hour later that I started feeling a bit odd. Very odd.

I tried eating my porridge but my hand was shaking so much I couldn't get the spoon to my mouth. And it wasn't just my hand: my whole body was trembling. Then I started shivering. It was one of our really hot days (remember them?) but I might as well have been sitting in a freezer.

I lay down, covered myself in thick blankets and fell asleep. When I woke up, I felt a bit light-headed but I'd stopped trembling. So no harm done?

Maybe not, but a friend who knows about these things warned me that some people can have an allergy to jellyfish stings, so it might be wise to avoid them in future. Shouldn't be a problem, I thought. We'd just find a bay free of them.

John Humphrys recounts a brush with a jellyfish off the Llyn Peninsula in north Wales File

Fat chance. They're everywhere this year. My daughter lives in Colwyn Bay, where there's a very long and lovely sandy beach. Perfect for dog walkers and swimmers. Until the invasion of the jellyfish.

They're floating in our seas and decomposing on our beaches. And they're not just disgusting, they can even hurt you when they're dead. Some of them, including the compass, have tentacles that can sting after they've been detached from the body.

All of which highlights a question that I have been pondering for many years. What is the point of jellyfish?

The world is full of nasty creatures, and many of them can be pretty unpleasant. Yet most of them serve a purpose. Mosquitoes cause a great deal of suffering but birds love them — especially swallows and martins.

At the other end of the food chain, a tiger in the wild wouldn't think twice about having us for lunch. But they're magnificent creatures. The world would be a poorer place without swallows and tigers.

As for the sea, it's home to the finest food on the planet, and even if you don't eat fish you can admire their beauty and their effortless elegance.

But jellyfish? They're just boring blobs of . . . well. . . jelly. They don't even have a brain. They just float around, carried hither and yon by the tide until they get washed up on the beaches and die. Or sting innocent swimmers like me.

They can even kill. Not very often admittedly, but why risk it? One fisherman in Wales told me he was getting reports from swimmers of a species of jellyfish called lion's mane appearing off Anglesey — and they pack a mighty sting that can land you in hospital.

They're big, too. Longer than a blue whale some of them. The Portuguese man o' war is not strictly a jellyfish but its sting is even worse and they make the occasional appearance in our waters too.

But the Al Capone of the jellyfish world is the Australian box. You don't mess with a box if you know what's good for you. Forget sharks, the box jellyfish is reckoned to be the deadliest creature in the sea.

And here's the thing that's so spooky about jellyfish. You can understand why a shark wants to eat you. He's hungry. Jellyfish don't get hungry — or not, at any rate, in any way we might understand. Not only do they have no brain, they have no heart either. Or blood. Or bones.

What they do have are receptors that detect light, vibrations and chemicals in the water. Intriguingly, they also have a sense of gravity. All of which means they can navigate from one patch of sea to another.

The experts reckon we are seeing more of them right now in our waters because our seas are getting warmer thanks to global warming. But no one really knows.

What we do know is that they are everywhere — from the freezing waters of the Arctic to the warm waters of the tropical oceans. They're not even limited to salt water.

Some species have been found in freshwater lakes and ponds — but there's probably no need to worry about your youngsters paddling in the local pond just yet.

I say 'just yet' in jest. But for all my disparagement of jellyfish, it's impossible not to respect them and to wonder what they might be getting up to in a few million years from now. Because it's a fair bet they will be doing their thing long after we humans have stopped offering them tempting targets.

My assailant was rather lovely. It was a compass jellyfish : about six inches in diameter, translucent, with dark orange lines radiating out from the centre of its bell. Less easy to spot were the tentacles stretching beneath it Stock

They are, quite simply, the greatest survivors on this planet there have ever been. Forget the dinosaur or the ancient bony fish which evolved more than 50 million years ago. Forget insects and trees and flowers and ferns and even fungi.

Jellyfish have roamed our planet's seas for at least 600 million years. That's long before the Permian-Triassic extinction some 250 million years ago, better known as the Great Dying.

It killed off more than 90 per cent of the species on Earth. But not the jellyfish.

And there's something else. As we pick our way around all those jellied corpses on the beach, we might pause to reflect that some of their cousins possess a power that we can only wonder at.

It is a power that makes them unique in the animal kingdom, that defies everything we have ever been taught about life. It is the power of immortality.

Sooner or later, every living creature dies because eventually its cells stop dividing. But there is one species that has been described by scientists as 'biologically immortal'. It is the only creature to which that description has ever been applied.

It is a tiny jellyfish called the Turritopsis dohrnii which lives in the Mediterranean Sea and in the waters of Japan. It is able to turn back time by reverting to an earlier stage in its life cycle.

So, yes, I have developed a new respect for these extraordinary creatures now that I know a bit more about them.

Even so, I shuddered a little when I saw the picture in these pages a few days ago of a fish trapped inside a compass jellyfish — the very species that gave me such a nasty turn.

The idea of a man-eating jellyfish may be the stuff of science fiction. But in a few million years . . ?