10 Fascinating Facts About the Portuguese Man O' War

The hazardous Portuguese Man O' War, with its potentially lethal sting, is frequently spotted along U.S. shorelines, creating challenges for beachgoers. Continue reading to discover more about these remarkable creatures.

1. The Portuguese Man O' War isn't a jellyfish.

While the Portuguese Man O' War may appear to be a swollen jellyfish, it is actually a siphonophore—a strange class of animals that form colonies of genetically identical individuals. These creatures begin as a fertilized egg, then grow by budding into distinct forms and organisms. The resulting tiny organisms, called polyps or zooids, are incapable of surviving alone, so they come together to form a tentacled mass. In this unified structure, they work together to travel and capture food.

Although the zooids within a Portuguese Man O' War are essentially clones, they take on different forms and have distinct functions [PDF]. Dactylozooids are long, hunting tentacles designed to capture prey; gastrozooids are smaller tentacles responsible for digesting the food; and gonozooids are reproductive entities that facilitate reproduction. Each Man O' War also has a pneumatophore, or 'float'—a large, bag-like polyp that serves as a gas-filled bladder and rests atop the colony. Capable of expanding and contracting, the float allows the colony to maintain buoyancy and harness the wind to move.

2. Bluebottles from the Indo-Pacific are close relatives.

When we mention the Portuguese Man O' War, we're referring to Physalia physalis, the siphonophore also known as the Atlantic Portuguese Man O' War, which inhabits warmer regions of the Pacific, Caribbean, Indian, and Atlantic oceans.

Another type of siphonophore that frequently stings beachgoers is the bluebottle, Physalia utriculus. Commonly referred to as the Indo-Pacific Portuguese Man O' War, it is found exclusively in the Pacific and Indian oceans. Smaller than its Atlantic relative, it hunts using a single, long tentacle.

3. The name Portuguese Man O' War likely refers to a type of naval vessel.

During the Age of Sail, numerous European navies utilized tall warships equipped with cannons and powered by the wind. British sailors referred to these types of ships as 'man of war.'

Physalia physalis colonies often spend a significant amount of time drifting at the water's surface. When their gas bladder is inflated, they resemble a sailboat, which is likely where the 'man o' war' name comes from. As for the 'Portuguese' part, 19th-century scientists speculated that sailors first encountered it near the Portuguese island of Madeira, while modern linguists believe the name stems from the ship's resemblance to the Portuguese version of a warship. Some also suggest that Renaissance sailors thought the pneumatophores resembled the helmets worn by Portuguese soldiers in the 16th century.

4. The tentacles of a Portuguese Man O' War can grow up to 165 feet long.

The dactylozooids can reach a maximum length of 30 feet, and are typically around that length. These tentacles are equipped with venomous cells that deliver excruciating, neurotoxic stings. If a tentacle is severed from the main colony, it might wash up on shore or float around for days until it eventually decomposes. Even a detached tentacle can sting you.

5. Portuguese Man O' War stings can be deadly to humans.

While the chances of dying from a Portuguese Man O' War sting are low, it doesn't mean you should take the risk of touching one. In 2018, 204 individuals in Hollywood, Florida, required medical treatment for stings, which can result in red welts, muscle cramps, increased heart rate, and vomiting.

In 1987, a person died after a cardiovascular collapse caused by getting too close to a Man O' War off eastern Florida. In 2010, a woman swimming near Sardinia was stung and died from what was believed to be anaphylactic shock.

6. Some fish make their home in Portuguese Man O' Wars.

Considering that small fish constitute about 70 to 90 percent of the Man O' War's diet, along with shrimp and other crustaceans, Nomeus gronovii, known as the Man O' War fish, is taking a considerable risk: It inhabits the siphonophore's tentacles despite not being immune to its stings. The fish skillfully weaves between the stingers. As juveniles, they consume plankton that drifts beneath their hosts, and as adults, they may occasionally snatch the Man O' War's prey or nibble on its tentacles.

7. Sea slugs appropriate the Man O' War's toxins.

The Portuguese Man O' War has numerous predators. Loggerhead sea turtles and ocean sunfish are known to feed on them. There are also blue dragon sea slugs, which not only feast on the Man O' War but also actively collect and store its toxins. By retaining the Man O' War's stinging cells within their skin, the blue dragons can use them as a defense against potential threats.

8. Portuguese Man O' Wars are known for their vibrant colors.

While translucent, the float often has hues of blue, pink, and/or purple [PDF]. To alert visitors of the presence of man o' wars (and other potentially dangerous marine creatures), beaches along the American Gulf Coast raise purple flags when these creatures are in the area.

9. Every colony has a specific gender.

The gonozooids of a man o’ war contain sacs that house either ovaries or testes, meaning each colony can be classified as male or female. While marine biologists aren't entirely certain how the man o' war reproduces, one theory suggests that the gonozooids release eggs and sperm into the open ocean, where fertilization occurs when these reproductive cells meet eggs or sperm from other colonies. This form of reproduction, known as broadcast spawning, is also practiced by various species of coral, sea anemones, jellyfish, and fan worms.

10. A collective of Portuguese man o’ wars is referred to as a legion.

The man o' war is not always seen alone. Massive groups, or legions, made up of over 1,000 colonies, have been observed drifting together. These creatures follow relatively predictable ocean currents and winds, making it possible to anticipate their arrival. For instance, the Gulf Coast experiences a distinct man o' war season during the winter months.