Do you like to swim in the sea? Perhaps, over the summer holidays, you visited a beach and went for a paddle. But if you’d done that in Wales or Cornwall over the last few days you may have encountered a dangerous animal. A shark? A killer whale? No – thousands of Portuguese men o’ war.
Portuguese men o’ war are a type of jellyfish with a painful and, in some cases, deadly sting. Unusually warm temperatures have brought them close to our coasts and, fearing that swimmers may be stung, Perranporth beach in Cornwall was closed this week.
So, what do we know about these deadly denizens of the deep? Here are the facts on the Portuguese man o’ war:
- Technically, they’re not jellyfish – they’re actually a collection of organisms called polyps, working together
- For all intents and purposes they are jellyfish though. They look just like them and come equipped with the jellyfish’s trademark sting
- Four polyps make up a man o’ war. The most prominent is blue, purple or pink and fills with air to keep the others afloat
- When it’s fully inflated the top polyp looks like the sail on an 18th Century Portuguese warship – hence the animal’s name
- The other three polyps deal with reproduction, feeding and defence. It’s these last ones that make up the animal’s sting
- Men o’ war’s stings can grow to lengths of up to 50 metres – that’s nearly twice as long as a blue whale!
- Though named the defensive polyp, the stings’ main job is to catch food. They stretch out through the water and paralyse small fish, squid or other prey
- They live in groups of up to a thousand individuals. That’s why our south-west coast has encountered so many of them
- If caught in a mass of Portuguese men o’ war a swimmer would be in trouble. People have been known to die after getting stung several times whilst trying to reach the shore
- More than 10,000 people are stung by men o’ war every year. The stings are very painful and cause welts on the skin which hurt for hours or even days
- Few people die from being stung though. Only severe reactions are fatal – much like with bee stings
- Even when a Portuguese man o’ war is dead it can still sting. Their venom remains potent for days, so if you find one washed up on the beach stay well away from it
Not all animals are in danger from Portuguese men o’ war. Some, like octopuses and sea turtles, are immune to their stings and specialise in eating them! In fact their liking for jellyfish, together with human pollution, has caused sea turtles problems. They often mistake plastic bags for jellyfish and these clog up their digestive systems. This can kill a turtle.
Dangerous as they are, in the big picture Portuguese men o’ war are not nearly as dangerous as us humans.
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