Portuguese Man-of-War Facts

Scientific Name: Physalia physalis

Atlantic Portuguese Man-of-War
Atlantic Portuguese man-of-war.

IDANIA LE VEXIER / Getty Images

With its colorful float and trailing stinging tentacles, the Portuguese man-of-war (Physalia physalis) might easily be mistaken for a jellyfish. However, a jellyfish is a single animal. The Portuguese man-of-war is a siphonophore, which is a colony of animals that function together and cannot survive apart. The creature's common name may come from its resemblance to a Portuguese sailing warship or to the helmets worn by Portuguese soldiers.

Fast Facts: Portuguese Man-of-War

  • Scientific Name: Physalia physalis
  • Common Names: Portuguese man-of-war, Portuguese man o' war, man-of-war
  • Basic Animal Group: Invertebrate
  • Size: The float is approximately 12 inches long, 5 inches wide; its tentacles can measure up to 165 feet
  • Lifespan: Probably 1 year
  • Diet: Carnivore
  • Habitat: Atlantic, Indian, and Pacific Oceans
  • Population: Abundant
  • Conservation Status: Not Evaluated

Description

The man-of-war has a distinctive sail-like float (pneumatophore) that may reach 12 inches in length and 5 inches in width, and rises 6 inches above the water surface. The colorful float may be translucent blue, pink, or violet. This gas bladder is filled with nitrogen, oxygen, argon, and a small amount of carbon dioxide from air, plus up to 14% carbon monoxide.

Portuguese man-of-war on a beach
Portuguese man-of-war on a beach. David Ziegler Getty Images

In addition to the pneumatophore, the man-of-war has three other polyp types. The dactylozooids are tentacles that are used for defense and disabling prey. The tentacles are blue or purple and can extend up to 165 feet. The gastrozooids are responsible for feeding. The gonozooids are used for reproduction.

Man-of-War vs. Blue Bottle

The genus Physalia includes two species: the Portuguese man-of-war and the Pacific man-of-war or Australian blue bottle (Physalia utriculus). The Portuguese man-of-war has a wider color range and many tentacles, while the Australian blue bottle is blue and has a single long tentacle.

Australian blue bottle on a beach
Australian blue bottle on a beach. Michelle Lehr / Getty Images

Habitat and Range

The species occurs in the warm waters of the Atlantic, Pacific, and Indian Oceans, as well as the Caribbean and Sargasso Seas. The Portuguese man-of-war lives on or just below the surface of the water. A siphon in the pneumatophore lets the animal float or descend in the water column. Wind pushes the animal's float at a 45 degree angle. Some individuals are "left-sided," while others are "right-sided." The different orientations of the floats help the animals to disperse across the oceans.

Diet

The Portuguese man-of-war is a carnivore. Its tentacles contain stinging cells called nematocysts that paralyze and kill small fish, worms, and crustaceans. The tentacles move prey to the gastrozooids on the underside of the float. The gastrozooids secrete enzymes that digest the prey. Nutrients are absorbed and circulated to other polyps. The man-of-war is prey to sea turtles, sea slugs, and crabs.

Reproduction and Offspring

The man-of-war life cycle includes a sexual and an asexual reproductive phase. Each colonial organism is either male or female. Spawning occurs mainly in the autumn. The gonozooids form gametes and release them into the water. The larva formed by the union of an egg and sperm then reproduces asexually by budding or mitotic fission until it achieves its mature form. This differs from the cellular division and differentiation of a non-colonial animal in that each type of polyp is a complete organism. However, a polyp cannot survive without other members of its colony. Like jellyfish and other Cnidarians, the rate of the life cycle depends on water temperature and other factors. It's likely the man-of-war lives to at least one year of age.

Conservation Status

The Portuguese man-of-war has not been evaluated by the International Union for Conservation of Nature (IUCN) for a conservation status. The species seems to be abundant throughout its range. Its population trend is unknown.

Portuguese Man-of-War and Humans

While the Portuguese man-of-war has no commercial value, it is of economic importance due to its impact on coastal tourism. Both jellyfish and man-of-war tentacles can sting after the animal is dead or when they are detached. Stings are painful, although not usually fatal. Neurotoxins in the venom cause mast cells in skin to release histamines, resulting in inflammation. Treatment typically involves tentacle removal, using vinegar or ammonia to inactivate remaining nematocysts, and soaking the affected area in hot water. Oral or topical antihistamines may be administered to combat inflammation.

Jellyfish sting
Jellyfish and man-of-war tentacles produce a characteristic rope-like sting.  4FR / Getty Images

Sources

  • Brusca, R. C. and G. J. Brusca. Invertebrates. Sinauer Associates, Inc., Publishers: Sunderland, Massachusetts, 2003.
  • Halstead, B.W. Poisonous and Venomous Marine Animals of the World. Darwin Press, 1988.
  • Kozloff, Eugene N. Invertebrates. Saunders College, 1990. ISBN 978-0-03-046204-7.
  • Mapstone, G. Global Diversity and Review of Siphonophorae (Cnidaria: Hydrozoa). PLOS ONE 10(2): e0118381, 2014. doi:10.1371/journal.pone.0087737
  • Wilcox, Christie L., et al. Assessing the Efficacy of First-Aid Measures in Physalia sp. Envenomation, Using Solution- and Blood Agarose-Based Models. Toxins, 9(5), 149, 2017. doi:10.3390/toxins9050149