information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

Portuguese man o' war (Physalia physalis)

Distribution data supplied by the Ocean Biogeographic Information System (OBIS). To interrogate UK data visit the NBN Atlas.



Each 'individual' Physalia physalis is composed of a group of polyps specialised for movement, catching prey, feeding and breeding. The individual polyps are dependent on each other for survival, each having a distinct role. A large, purple, gas filled float (the pheumatophore) reaching up to 30 cm in height allows Physalia physalis to float on the surface. The crest running along the top of the pheumatophore acts as a sail when raised. The jellyfish has many digestive polyps (gastrozooids), which hang down and secrete digestive juices onto the prey that has been caught and immobilised by the sting of the long, contractile tentacles (the dactylozooids). The tentacles may hang down several meters and have a bead-like appearance. Each 'bead' contains specialised stinging cells (nematocysts), which produces a debilitating sting.

Recorded distribution in Britain and Ireland

Physalia physalis is common in the warm waters of the Atlantic. However, individuals are sometimes driven by prevailing winds to the coasts of Britain and Ireland, especially southwest coasts.

Global distribution



A pelagic warm water species driven into to shore by winds and currents.

Depth range


Identifying features

  • Physalia physalis has a single, highly distinguishable, gas filled float (the pheumatophore), unlike many other siphonophores which rely on a group of swimming bells for floatation.
  • Physalia physalis has contractile tentacles that can reach 10-20 m in length when extended.
  • The crest of the purple float has a shot of pink running through it.

Additional information

Even though individual Physalia physalis are not an unusual sight on the coasts of Britain and Ireland, mass standings are uncommon, occurring only 3 or 4 times a century (Wilson, 1947). The sting of Physalia physalis causes severe pain, skin lacerations, convulsions, respiratory distress and in some cases death (Williamson et al., 1996). The sting remains potent even after death and the tentacles should not be touched. Portuguese man o'war are carnivorous feeding mainly on small crustaceans and larval fish (Kirkpatrick & Pugh, 1984).

Listed by

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Further information sources

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  1. Crothers, J. A., 1997. A key to the major groups of British marine invertebrates. Field Studies, 9, 1-177.

  2. Howson, C.M. & Picton, B.E., 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]

  3. Kirkpatrick, P.A., & Pugh, P.R., 1984. Siphonophores and Velellids London: Academic Press. [Synopses of the British Fauna No. 29.]

  4. National Biodiversity Network (NBN) Atlas website. Available from:  Accessed 01 April 2017

  5. Ruppert, E.E. & Barnes, R.D., 1994. Invertebrate zoology (6th ed.). Fort Worth, USA: Saunders College Publishing.

  6. Williamson, J.A., Fenner, P.J., Burnett, J.W. & Rifkin, J.F., 1996. Venomous and poisonous marine animals: a medical and biological handbook. Sydney: University of New South Wales Press.

  7. Wilson, D.P., 1947. The Portuguese man-o-war, Physalia physalis L. in British and adjacent seas. Journal of the Marine Biological Association of the United Kingdom, 27, 139-172.


This review can be cited as:

Heard, J.R. 2006. Physalia physalis Portuguese man o' war. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 24-02-2018]. Available from:

Last Updated: 20/10/2006