10 Facts About the Portuguese Man O' War

Something a lot scarier than any Jersey Devil has been washing up on beaches in the Garden State lately: This month, the dangerous Portuguese Man O’ War—which has a potentially deadly sting—has been sighted in Cape May and Wildwood, New Jersey, which could lead to problems for beachgoers. Read on to learn more about these unusual creatures.

1. IT'S NOT A JELLYFISH.

The Portuguese Man o’ War may look like a bloated jellyfish, but it’s actually a siphonophore—a bizarre group of animals that consist of colonies made up of dozens, hundreds, or even thousands of genetically-identical individual creatures. A siphonophore starts out as a fertilized egg. But as it develops, it starts "budding" into distinct structures and organisms. These tiny organisms—called polyps or zooids—can’t survive on their own, so they merge together into a tentacled mass. They must cooperate as one in order to do things like travel and catch food.

Though the zooids within a Man O’ War are basically clones, they come in different shapes and serve different purposes [PDF]. Dactylozooids are long hunting tentacles built to ensnare prey; gastrozooids are smaller tentacles which digest the food; and gonozooids are dangling entities whose job is to facilitate reproduction. Every Man O’ War also has a pneumatophore, or “float”—an overgrown, bag-like polyp which acts as a giant gas bladder and sits at the top of the colony. Capable of expanding or contracting at will, it provides the Man O’ War with some buoyancy control. An expanded float also enables the colony to harness winds to move around.

2. A CLOSE RELATIVE IS THE INDO-PACIFIC “BLUEBOTTLE.”

When we say “Portuguese Man O’ War,” we’re talking about Physalia physalis, the bizarre siphonophore that’s scaring New Jerseyans right now. Also known as the Atlantic Portuguese Man O’ War, it can be found in warmer parts of the Pacific, the Caribbean, the Indian Ocean, and of course, the Atlantic.

Another kind of siphonophore which regularly stings beachgoers is the so-called bluebottle, Physalia utriculus. It’s sometimes called the Indo-Pacific “Portuguese” Man O’ War and is restricted to the Pacific and Indian Oceans. It’s smaller than the Atlantic species and unlike its bigger counterpart—which has multiple hunting tentacles—it hunts with a single, elongated tentacle.

3. THE NAME “PORTUGUESE MAN O’ WAR” IS PROBABLY A NAVAL REFERENCE.

In the age of sailing, many European navies used tall warships loaded with cannons and propelled by three masts. British sailors took to calling this kind of vessel a “Man of War.”

What does that have to do with Physalia physalias? These colonies spend a lot of time floating at the water’s surface, and when the gas bladder is expanded, it looks—and acts—a bit like a sailboat, hence the “Man O’ War.” As for the Portuguese part, 19th century scientists proposed that sailors encountered it near the Portuguese island of Madeira, while modern etymologists tend to think that it looked like the Portuguese version of the ship.

Or at least that’s one explanation for the creature’s peculiar name. It’s also been suggested that Renaissance-era sailors thought the pneumatophores resembled the helmets worn by Portugal’s soldiers during the 16th century.

4. MAN O’ WAR TENTACLES CAN BE UP TO 165 FEET LONG.

At least, that’s the maximum length for the dactylozooids—which are normally around 30 feet long and use venom-spewing cells to deliver painful, neurotoxic stings. When a tentacle is detached from the rest of the colony, it might wash ashore somewhere or drift around for days on end until it decomposes. Be warned: Even a severed tentacle can sting you.

5. ON RARE OCCASIONS, STINGS CAN BE FATAL TO HUMANS.

The odds of being killed by a Portuguese Man O’ War are slim. But just because deaths are rare doesn't mean you should touch one: On February 11, 2018, 204 people in Hollywood, Florida were treated for stings, which can lead to red welts on the skin, muscle cramps, elevated heart rates, and vomiting.

Still, the creatures can kill: One unlucky victim suffered a full cardiovascular collapse and died after getting too close to a Man O’ War in eastern Florida back in 1987. More recently, a woman swimming off Sardinia was stung by one and died of what was believed to be anaphylactic shock.

6. SOME FISH LIVE IN THEM.

Given that tiny fish make up about 70 to 90 percent of the Man O’ War’s diet (it also eats shrimp and other crustaceans), Nomeus gronovii, a.k.a. the Portuguese Man O’ War Fish, is playing a dangerous game: It lives among the siphonophore's tentacles even though it's not immune to its stings, swimming nimbly between the stingers. Young fish eat planktons which wander under their hosts and, as they get older, will sometimes steal the Man O’ War’s prey—or nibble on its tentacles.

7. SEA SLUGS LIKE TO STEAL THEIR TOXINS.

The Man O’ War has a long list of enemies. Loggerhead sea turtles and the bizarre-looking ocean sunfish are thick-skinned enough to eat them. There are also “blue dragon” sea slugs, which not only devour the Man O’ War but actively harvest and appropriate its toxins. After storing Man O’ War stinging cells in their own skins, the blue dragons can use it as a predator deterrent.

8. MAN O’ WAR COME IN PRETTY COLORS.

Although it’s translucent, the float is usually tinted with blue, pink, and/or purple hues. Beaches along the American Gulf Coast raise purple flags in order to let visitors know when groups of Man O’ War (or other potentially deadly sea creatures) are at large.

9. EVERY COLONY HAS A SPECIFIC SEX.

The Man O' War's gonozooids have sacs that house ovaries or testes—so each colony can therefore be considered “male” or “female.” Though marine biologists aren’t completely sure how the Man O’ War procreates, one theory is that the gonozooids release eggs and sperm into the open ocean, which become fertilized when they cross paths with floating eggs or sperm from other Man O’ War colonies. This “broadcast spawning” method of reproduction is also used by many species of coral, fan worms, sea anemone, and jellyfish.

10. LOOK OUT FOR MAN O’ WAR LEGIONS.

The Man O’ War isn't always seen in isolation. Legions consisting of over 1000 colonies have been observed floating around together. Because they drift along on (somewhat) predictable winds and ocean currents, it’s possible to anticipate where and when a lot of the creatures will show up. For example, the Gulf Coast’s Man O’ War season arrives in the winter months.