Head to head
Lion's Mane Jellyfish vs Portuguese Man o' War
A Portuguese man o' war looks like a jellyfish, floats like a jellyfish, and stings like a jellyfish, and it is very often called one. But it is not a jellyfish. It is a siphonophore, a floating colony of many specialised individual animals, called zooids, that cannot survive alone and function together as one. A true jellyfish, such as the lion's mane, is a single animal.
| Lion's Mane Jellyfish | Portuguese Man o' War | |
|---|---|---|
| What it is | A single animal, a true jellyfish (a cnidarian medusa) | A colony of many specialised animals living as one |
| Body | A pulsing bell with trailing tentacles | A gas-filled float above the water, with tentacles below |
| Movement | Weak swimming by pulsing the bell | None; drifts with wind and current |
| Size | Bell up to about 2 m; tentacles tens of metres | Float 15–30 cm; main tentacle often 10 m, sometimes 30 m |
| Sting | Painful, rarely serious | Severe, whip-like welts; occasionally causes systemic illness |
| Survives being broken up | No | The colony cannot, but the pieces are still venomous |
| Where you meet it | Cool northern seas | Warm and temperate open ocean; blown ashore in groups |
| Predators | Sea turtles, ocean sunfish, some seabirds | Sea turtles, the blanket octopus, the violet sea snail |
Jellyfish vs Portuguese Man o' War: common questions
Is a Portuguese man o' war a jellyfish?
No, although it is almost always called one. A jellyfish is a single animal. A man o' war is a siphonophore, a colony made up of many separate small animals, each doing a different job, one forming the float, others catching prey, others digesting, others reproducing, and none of which can live on its own. They belong to the same broad group as jellyfish, the cnidarians, which is why they share stinging cells, but a man o' war is closer to a coral colony in organisation than to a jellyfish.
Which sting is worse?
A Portuguese man o' war sting is generally the more severe. It causes immediate intense pain, long whip-like welts, and in some people nausea, fever, and, rarely, breathing or heart problems that need medical care. A lion's mane jellyfish sting is painful and can leave a rash and blistering, but for most people it is unpleasant rather than dangerous. Both can sting from tentacles that have broken off and are lying in the water or on the sand.
How do you treat one of these stings?
Get out of the water, carefully pick or scrape off any tentacles without rubbing, and rinse the area with seawater or, for many species, vinegar, but not fresh water, which can make undischarged stinging cells fire. Immersing the area in water as hot as can be tolerated, or a hot shower, helps with the pain. Seek medical help for a large sting, a sting to the face, or any breathing difficulty, chest pain, or collapse.