Beachgoers’ information to recognizing ‘nasty’ jellyfish – carry vinegar and do not wee

It’s that time of year when fascinating and sometimes dangerous creatures start to invade our shores.

But what should you do if you spot a stranded jellyfish and can they still sting you when they are dead? Here we have the answers to all your burning questions as Frankie Hobro, director of Anglesey Sea Zoo in North Wales explains…

Love them or hate them, jellyfish are intriguing creatures that fulfil an essential role in the oceanic food web. They rely entirely on currents to carry them around so they generally appear in large numbers.

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But with so many benign species being easily mistaken for the more nasty ones, and vice versa, the golden rule is always look but don’t touch. Whilst in the water you should also keep your distance – the tentacles often drift a long way behind the main body of the animal, which is what makes them such effective predators.

Watch out for the stingers

The harmless By-The-Wind-Sailors bear a great similarity to their much maligned and much larger relative the Portuguese Man O’ War.

Both have a float above the surface with a striking bluish purple ‘sail’ to catch the wind.

Most impressive in size among our common species are lionsmane and barrel jellyfish, both of which frequently grow to the size of a dustbin lid or larger and are a staple food for our native leatherback turtles.

The barrel jellyfish is harmless to humans but is still a formidable sight, a dense white mass with short tentacles which often grow to the size of a barrel, hence their name.

Similarly the lionsmane jellyfish reaches 2m in diameter and gives a very nasty sting, along with the similar but smaller compass jellyfish.

Sea gooseberries are possibly the most fascinating jellies of all.

These appear as benign and boring looking small blobs of jelly on the beach but sparkle with rainbow iridescence when in the water.

Despite their delicate, almost ghostly appearance, and the fact that they are harmless to humans, they are voracious predators in the marine world, feeding on fish eggs, larvae, and many other small marine animals including each other.

Getting stung

When you think there may be jellyfish in the sea it’s always best to be safe by wearing a full length wetsuit, ideally with bootees or swim shoes to cover feet and ankles, even whilst paddling.

If you are unfortunate enough to get stung, the best thing to do is to douse the whole area thoroughly with vinegar as this immediately disables the stinging cells. Concentrated lemon juice will also work.

Contrary to popular belief, peeing on it is unlikely to give any relief, and may even make it worse by triggering more stinging cells. This is due to the way the stinging cells on a jellyfish work.

A single tentacle may contain thousands of stinging cells, called nematocysts. Each cell contains a tiny stinging dart which shoots out to inject the venom and this is triggered by osmosis.

So any tiny change in pressure to the wall off the cell will cause this toxic arrow to shoot out, independently of the jellyfish itself, which is why the nematocysts can continue to function long after the animal is dead.

A strong acid such as vinegar or lemon juice destroys the cells and denatures the venom on contact so this is by far the safest way to prevent and treat stings.

A far better alternative to peeing, if you don’t have vinegar or lemon juice handy, is to rinse the affected area with clean sea water (not fresh water) until all pieces of the tentacles have been removed from the skin, as they can continue to sting long after they are separated from the body of the animal.

A credit card is useful to assist with this as they are flexible enough to scrape the sticky pieces of tentacle off the skin whilst avoiding accidental contact with a bare hand.

Of course if in any doubt or with any serious encounters, seek professional medical assistance immediately, as a large number of stings simultaneously or those from a particularly large jellyfish can cause severe pain, swelling and occasionally a severe reaction such as anaphylaxis.

The worst of the lot

One particular jellyfish to be wary of during our warmer months is the Portuguese Man O’ War. Until recently these were rare vagrants in the British shores and the few that arrived here were usually juveniles.

However, increasing sea temperatures and the changes in the Gulf Stream and Atlantic currents caused by global warming are resulting in many more, much larger individuals turning up here regularly, and last summer especially there were more sightings of these than ever, both washed up on our shores and out at sea. With our seas becoming warmer sooner and for longer each year, this trend is likely to continue.

The Portuguese Man O’War is in fact not a true jellyfish, although it looks like one, it is a siphonophore, which is actually a colony of animals working together to make a single individual.

They do not swim, but use ocean currents to get carried around as their float acts like a sail allowing them to get carried for thousands of miles, dragging their long tentacles behind them underwater, which deliver a venomous sting, deadly to fish and other marine creatures.

They are named after their resemblance to 18th century Portuguese warships, and the distinctive blue float on the surface of the water can be up to 15cm tall, while the tentacles below the water which commonly reach at least 10m in length and can be as long as 30m, are found trailing behind the animal beneath the surface.

While the Portuguese Man O’War cannot be considered ‘deadly’ to humans, their sting is excruciatingly painful.

The Portuguese Man O’War is a fascinating and extremely beautiful creature and it is very tempting to get up close to observe them but this should be avoided at all costs.

Dead Portuguese Man O’ War and their detached tentacles are still capable of stinging just as painfully for hours or even days so they should be avoided when stranded on the shore.

The vast majority of jellyfish stinging incidents in Britain are very minor so it is important that jellyfish don’t put people off enjoying our beaches and the sea.

But next time you have fish and chips at the beach, remember to stash some extra vinegar sachets in your first aid kit.

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