Meet the Portuguese Man o’ War: One of the deadliest and weirdest creatures in the ocean

Portuguese Man o’ War (Image Credit: instagram.com/rafa.mesquita/)

The ocean is home to countless fascinating species, but few are as deadly and strange as the Portuguese Man o’ War (Physalia physalis). Often mistaken for a jellyfish, the Portuguese Man o’ War is far more than a single creature—it’s a floating colony of specialized organisms. This notorious marine siphonophore, named for its resemblance to 18th-century Portuguese sailing warships, is both mesmerizing and perilous.

Recently, marine footage captured near Bertioga, close to Guaratuba beach in Brazil, revealed the striking presence of these creatures. Posted on Instagram by Rafael Mesquita Ferreira (@rafa.mesquita), the video shows Portuguese man o’ war drifting close to the surface, their vibrant sails catching the light while their long, venomous tentacles trail below in mesmerizing motion.

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A post shared by Rafael Mesquita Ferreira (@rafa.mesquita)

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What is Portuguese Man o’ War?

Unlike solitary jellyfish, the Man o’ War is composed of zooids—tiny, genetically identical individuals specialized for tasks such as floating, feeding, hunting, and reproduction. Together, they function as one organism.

At the surface, a gas-filled bladder called the pneumatophore acts like a sail, carrying this colony across oceans by wind and currents. Beneath, long tentacles—often spanning 10 to 30 meters (30 to 100 feet)—linger, equipped with cnidocytes: stinging cells that fire venomous nematocysts capable of paralyzing small fish and causing excruciating pain in humans.

Though rarely life-threatening, stings from the Man o’ War can leave painful welts, induce allergic reactions, and in extreme cases, cause severe systemic effects. Notably, their tentacles remain dangerous even after the creature has washed ashore.

Strong winds and currents often push these creatures toward coastlines, leading to mass strandings. Once they wash ashore, even a translucent, deflated body can retain its sting—prompting authorities to close beaches to protect unsuspecting beachgoers.

Interestingly, some tiny fish species, like the Man-of-War fish (Nomeus gronovii), share a risky symbiosis by living near the tentacles to avoid predators. They're not immune to the venom, so they rely on extreme caution and swift movement.

The Portuguese Man o’ War remains one of the ocean’s most enigmatic creatures—both stunning and sinister.