8 Fantastic Facts About the Portuguese Man-of-War

It isn't a jellyfish, and isn't even a single organism.

Portuguese man-of-war on a beach in the Florida Keys
This Portuguese man-of-war washed onto a beach in the Florida Keys.

4Neus/Flickr/CC BY 2.0

With its mohawk-like feature, the Portuguese man-of-war is a decidedly punk-rock sea creature. But that's just one of the many odd and interesting facts about this organism — or should we say organisms?

1. The Portuguese Man-of-War Is Four Organisms Working as One

The man-of-war may appear to be a single organism, but it's four different organisms, or zooids, that can't function without each other. Each one provides a necessary function for the others to survive.

The top zooid, which resembles a blob with the aforementioned mohawk, is the pneumatophore. It's basically a gas-filled bag that allows the man-of-war to float. The next two zooids, gastrozooids and dactylozooids, are the man-of-war's tentacles. The former, as their name implies, are the organism's feeding tentacles. The latter are for defense and capturing prey. The final zooid, gonozooids, deal with reproduction.

2. It Was Named for Its Resemblance to Ships

over/under view of Portuguese man-of-war at the ocean surface
The man-of-war relies on its sail to move through the ocean. Stephen Frink/Getty Images

That mohawk is also how the man-of-war got its name. It resembles ships the Portuguese navy used in the 18th century when they were at full sail. The name also may refer to the topped helmets Portuguese soldiers wore during the same period.

3. The Portuguese Man-of-War Isn't a Jellyfish

A jellyfish is a single organism, not multiple ones combined into one. The man-of-war is, as a result, a completely different species called Physalia physalis. Men-of-war and jellyfish belong to the same phylum, Cnidaria, but then so do 10,000 other animals.

4. It Delivers a Horrible Sting

A dead Portuguese man-of-war on a beach
The tentacles of a Portuguese man-of-war can grow to be 165 feet long. Roberto La Rosa/Shutterstock

It may not be a jellyfish, but the man-of-war does have one trait we commonly associate with jellyfish: painful stings. The dactylozooids are covered in venom-filled nematocysts, which is how men-of-war kill their prey, typically small fish and plankton. The stings are painful to humans, but are rarely fatal.

With tentacles that can reach up to 165 feet (50 meters), getting wrapped in them can leave you looking like you've been struck with a whip. Treatments for the stings have been hotly debated, but a 2017 study in the journal Toxins recommended vinegar to wash away any remaining nematocysts once the tentacles are removed and then soaking the affected area in hot water, ideally 113 degrees Fahrenheit (45 degrees Celsius) for around 45 minutes.

5. It Does Have Predators

Portuguese men-of-war grouped closely together
Portuguese men-of-war may be found in isolation or in large congregations. NFKenyon/Shutterstock

Despite its sting, the tables do turn on the man-of-war. The loggerhead turtle and the ocean sunfish both gobble up Physalia physalis, which isn't too surprising as both species also eat jellyfish. Also notable among its predators is the blanket octopus. This large octopus has been sighted with tendrils of defeated men-of-war attached to their suckers, likely using them for both offense on prey and defense against predators. The 1.5-inch (4 cm) blue dragon sea slug is another man-of-war predator, ingesting the venomous nematocysts and storing them in its finger-like cerata.

6. Some Brave Fish Live Among Its Tentacles

The man-of-war fish, also known as the bluebottle fish, lives near the ocean floor during adulthood, but in its youth braves the dangerous tentacles of Portuguese men-of-war. Unlike some animals that rely on immunity or physical protection from their venomous landlords — like clownfish, some of which have mucus to protect them from sea anemones — these young fish seem to mainly rely on sheer agility to physical dodge the nematocysts. The daring juveniles eat small pelagic invertebrates and may nibble on the man-of-war's tentacles.

7. It Goes With the Flow

Portuguese man-of-war on a beach on Portugal
A Portuguese man-of-war lies on the beach after washing ashore in Algarve, Portugal. Bruno Guerreiro/Getty Images

The man-of-war has no means of propulsion, so it simply drifts, either riding the currents of the ocean or sailing as its pneumatophores catch the sea breeze. If there's a threat on the surface, the creature can temporarily deflate its pneumatophore to sink below the water.

8. The Portuguese Man-of-War Washes Up on Shores a Lot

Perhaps because of how it moves, the man-of-war washes up on beaches all over the world, from South Carolina to Britain to Australia. When a group of them showed up along Britain's southern coast by the thousands in 2017, an expert from the Marine Conservation Society cited "a combination of factors" to explain the men-of-war's presence, including hurricanes. Even if they're not in the ocean, men-of-war can still sting you, so avoid them if they're washed up on the beach.