The Portuguese Man-of-war Is Not a Jellyfish and Packs a Nasty Sting

By: Mark Mancini  | 
The Portuguese man-of war (Physalia physalis) has a network of tentacles that can measure anywhere between 30 feet (9 meters) and 100 feet (around 30 meters) long. Wild Horizons/Universal Images Group/Getty Images

Don't ignore purple flags at the beach. When American lifeguards fly them, it's because potentially dangerous sea creatures have appeared in the water.

Maybe there's a gang of jellyfish close by, or perhaps some stingrays are on the move. But a purple flag can also signal the arrival of a much weirder life form: Physalia physalis, a venomous drifter commonly known as the Portuguese man-of-war.


Out of Many, One

The Portuguese man-of-war (sometimes spelled "man-o'-war") is partly transparent, lacks a spine and kills prey with stinging tentacles. If you didn't know any better, you might mistake this thing for a jellyfish.

But it's not. Indeed, there's a fundamental difference between them. Every jellyfish is a singular animal, just like you or me. On the other hand, every Portuguese man-of-war is a floating colony made up of smaller, genetically identical entities that all live and work together in concert.


"The Portuguese man-of-war is colonial and the colony consists of bodies (called zooids)," says biologist Catriona Munro, in an email. She tells us that from an evolutionary standpoint, these bodies are similar "to free living individuals."

Their lifestyle isn't all that unique. The Portuguese man-of-war is a siphonophore; it belongs to the Siphonophora order of animals. And when you get right down to it, all known siphonophores, this species included, are just colonies of zooids.

"The colony itself functions as an 'individual' and the bodies or units within the colony do not," explains Munro.


Zooids On Parade

"In general, the [Portuguese man-of-war] is comprised of several types of zooids with specific functions," says Paul Bologna of Montclair State University in Montclair, New Jersey, in an email. As he puts it, "Hundreds to thousands of individual zooids might comprise the whole colony," depending on the size of the man-of-war at hand.

Some of them, the "gastrozooids," break down food for the colony. That food is captured in the first place by the grasping "dactylozooids," also known as "tentacular palpons." Another important player is the "pneumatophore," a gas-filled flotation bladder.


And let's not forget about the procreation specialists.

Human beings might not have too many things in common with Portuguese men-of-war. Yet they, like us, reproduce sexually. Every colony produces sperm or egg cells — but not both.

"During reproductive seasons, individuals shed their gametes [sex cells] into the water where fertilization of the eggs occurs," Bologna says. (Note that in this context, the word "individual" refers to an entire colony. We're not talking about lone zooids here.)

"These cells begin to divide and develop in the water column," Bologna continues. "As the individual grows, new zooids (clones within the colony) are generated. As the early colony develops, the pneumatophore expands and fills with air, which brings it to the surface where final development and growth occurs."


Come Sail Away

Have pneumatophore, will travel. Once inflated, this specialty air sac kind of resembles a deformed party balloon.

It's how the creature gets around. Unlike octopuses or true jellyfish, Portuguese men-of-war can't actively swim. The species must instead rely on its bloated pneumatophore, which pokes out above the surface of the water and catches the wind like a ship's sail, propelling the whole colony forward.


Geography has very little to do with the name "Portuguese man-of-war," by the way; the critter doesn't have any special connection to Portugal. No, people call it that because of the animal's distinctive sailing mechanism. "The common name in English comes from their likeness to 15th-century Portuguese war ships," says Munro.

Tropical waters are the usual domain of this species. But pay heed: Every so often, winds and currents sweep Portuguese men-of-war into more temperate places.

"In the northern Atlantic Ocean, Portuguese men-of-war often get carried north with the Gulf Stream current off the coast of the United States, so it is common to see them wash up on beaches from [South Carolina] to Maine. Additionally, the Gulf Stream continues across the Atlantic, so they wash up along the coast of England and northern European countries quite frequently," notes Bologna.

Over in the Indo-Pacific, there's a smaller — but otherwise similar-looking — siphonophore called the "bluebottle." There's been some debate about whether or not it belongs to the same species as the Portuguese man-of-war.

The so-called 'Floating Terror,' or Portuguese man-of-war, has long tentacles that can cause a painful sting, which can be fatal in extremely rare cases, even days after it has washed up on the beach and died.
Matt Cardy/Getty Images


A Venomous Brew

Beneath the man-of-war lies a network of tentacles, capable of measuring 30 feet (9 meters) or even upward of 100 feet (around 30 meters) long.

They're loaded with the invertebrate's not-so-secret weapon: stinging cells.


"Within each of these cells is a harpoon-like structure (organelle) called a nematocyst, whose function is to release and penetrate the 'skin' of another organism and then release its cocktail of venoms," Bologna says. Injection can paralyze the fish, crustaceans and other small animals this carnivore devours.

People aren't on the menu, but beachgoers should keep their distance. The sting of a Portuguese man-of-war can trigger agonizing skin pain. Other symptoms might include abdominal pain, vomiting, headaches and diarrhea. Human fatalities are rare, but not unheard of.

"Most people who have had severe encounters with them, have had close contact in open water when the trailing tentacles wrap around arms and legs where significant numbers of stinging cells are discharged," notes Bologna.

Beached men-of-war can sting you too, so exercise caution if you ever see one lying on the shore.


Treating Stings

Researcher Angel Yanagihara from the University of Hawaii at Mānoa was part of a team that compared different treatment strategies for Physalia stings in a 2017 study.

"First aid for the man-of-war is a bit controversial. Vinegar is generally recommended as a first step to prevent additional discharge of ... nematocysts left on the skin," Yanagihara says in an email.


What's step no. 2? Your most practical option might be to immerse the affected area in "skin-safe hot water" with a temperature of 107.6 to 113 degrees Fahrenheit (42 to 45 degrees Celsius) for 30 to 45 minutes. Applying an equally warm "hot pack" for that amount of time should also do the trick.

"Better outcomes have been documented using StingNoMore spray followed by StingNoMore cream. These contain patented components that specifically inhibit venom after it has been injected into the skin better and faster than the application of heat," says Yanagihara.

One thing you definitely shouldn't do is pee on the injury.

Urine is sometimes touted as a folk remedy for jellyfish and Portuguese man-of-war stings. A 1997 episode of the sitcom "Friends" popularized this idea. Don't buy it. "Scientific studies have not shown that urine reduces venom activity or tissue damage," Yanagihara says.