Portuguese man o' war

Man o' wars float in the warm Atlantic Ocean.

The wind blows them along. Sometimes there are lots of them together. Sometimes the wind pushes them onto beaches.

Man o' wars float on the surface of warm seas. They cannot swim at all: the wind and the ocean currents carry them. Sometimes they drift together in huge groups of 1,000 or more.

Scientists recently found that man o' wars around the world belong to several different species. The Portuguese man o' war itself lives in the Atlantic Ocean, including the waters off New England, Bermuda, Florida and Texas and across to the coasts of Europe. Its close relatives, other man o' war species, live in the Pacific and Indian Oceans.

Older accounts treat all man o' wars as one species found in the Atlantic, Pacific and Indian Oceans, the Caribbean and the Sargasso Sea (ADW), mostly in tropical and subtropical seas (NOAA). Church and colleagues (Current Biology, 2025) found P. physalis in the strict sense in the North and Southwest Atlantic, while P. utriculus occurs in the Pacific, Indian, Southwest Atlantic and Gulf of Mexico, P. megalista in the southern Pacific, Indian and Southwest Atlantic, and P. minuta around New Zealand, Tasmania and eastern Australia.

Their drift models suggested that P. physalis collected off Ireland, Spain, the Azores and the Canary Islands had probably come from the central North Atlantic, and that specimens from New England, Bermuda, Florida and Texas were genetically similar, linked by the Gulf Stream. The map shades the Atlantic Ocean.

Man o' wars mostly eat small fish.

Their long tentacles hang down in the water like fishing lines. When a fish swims into them, the tentacles sting it and pull it up to be eaten.

A man o' war is like a floating fishing boat. Long tentacles hang below the float, about 10 meters on average and sometimes as long as 30 meters. They are covered in tiny stinging capsules that stop small fish and shrimp from moving.

Most of what it eats, 70 to 90 percent, is fish, especially young fish. The tentacles pull the catch up to the feeding polyps under the float. These polyps have their own mouths, and they digest the food and share it with the whole colony.

Dactylozooids carry cnidocytes; NOAA describes nematocysts as microscopic capsules with coiled, barbed tubes whose venom can paralyze and kill small fish and crustaceans. ADW reports a diet mainly of fish fry and small adult fish, with shrimp, other crustaceans and plankton; nearly 70 to 90 percent of prey are fish, and larger fish such as flying fish and mackerel are sometimes caught, though they usually escape.

Prey is digested in the bag-like gastrozooids along the underside of the float, each with its own mouth. They secrete enzymes that break down proteins, carbohydrates and fats; indigestible remains are pushed out through the mouths, and nutrients circulate to the other polyps of the colony.

A man o' war cannot swim. It sails!

The wind pushes its crest, and the sea carries it far away. Some sea animals, like the blue dragon, eat man o' wars.

A man o' war cannot swim against the current, but by sailing with the wind it can drift a very long way. Scientists who modeled their drift found that most stay in one part of the ocean, carried by big currents such as the Gulf Stream, though a few travel far. Huge groups sometimes drift together, and when the wind blows toward land for days, many wash up on beaches.

Some animals eat man o' wars despite the stings. The tiny blue dragon sea slug eats them and even keeps their stinging cells for itself, and some fish and crabs eat them too.

Locomotion is passive: the colony cannot swim and is driven by wind and current via its float and crest (ADW). Church and colleagues hindcast drift paths and found that, despite this mobility, populations are structured by ocean region, following major current systems such as the Gulf Stream, with a few individuals showing long-distance dispersal between regions.

Predators include some fish and crustaceans such as the sand crab (ADW), and the nudibranch Glaucus atlanticus, which stores Physalia nematocysts in its cerata (Sea Slug Forum, Australian Museum).

There are lots of man o' wars. They are not in danger.

Their tentacles sting. If you see one in the sea or on the sand, look but do not touch. Tell a grown-up.

The Portuguese man o' war has not been assessed for the IUCN Red List, and it is not rare. Because scientists have only just found that there are several kinds of man o' war, there is still a lot to learn about each one.

Its sting is very painful, and NOAA warns that a man o' war washed up on the beach can still sting you even weeks later. The safe rule: look with your eyes, never touch, and tell a grown-up if you see one.

Physalia physalis is listed as Not Evaluated on the IUCN Red List (ADW; GBIF's Red List copy), and ADW notes it is not especially rare or in need of special conservation effort. The 2025 species split means the range, abundance and biology of each Physalia species now need fresh study.

NOAA states that the sting is rarely deadly to people but very painful and causes welts on exposed skin, and that stranded animals may still sting weeks after washing ashore. ADW notes the cnidocytes keep their potency long after stranding and that stings cost coastal areas money in treatment each year.