Fast Facts: Blue Bottles

  • The bluebottle (Physalia utriculus) is sometimes confused with its larger, more venomous Atlantic cousin, the Portuguese Man o’ War.
  • It is a common summer visitor to Sydney beaches.
  • In Sydney, it is the north eastern winds and warmer currents, that bring them to beaches on the incoming tides.
  • The Bluebottle is really a colony of four kinds of highly modified individuals (zooids). The zooids are dependent on one another for survival.
  • Within the colony, specialised polyps make up the float, tentacles, digestive system and reproductive organs.
  • The float is a single individual and supports the rest of the colony.
  • The tentacles are polyps concerned with the detection and capture of food and convey their prey to the digestive polyps.
  • The float is a bottle or pear-shaped sac that can exceed 15 cm.
  • It is mainly blue, though its upper margin may show delicate shades of green or pink.
  • It is a living, muscular bag that secretes its own gas, which is similar to air.
  • The float has aerodynamic properties.
  • It sails at a slight angle downwind and the course is determined by the curvature of the float and the underwater resistance of the rest of the colony.
  • The float may project either to the left or to the right; the left-handed forms sail to the right of the wind and vice versa.
  • If the sailing angle of one form leads to its stranding on the shore, the others sailing to the opposite side of the wind may escape.
  • The Bluebottle belongs to the phylum Cnidaria, which includes corals and sea anemones.
  • Bluebottles feed mostly on larval fish, molluscs, surface plankton and small crustaceans such as copepods and amphipods.
  • The most impressive members of the colony are the tentacles.
  • As it drifts downwind, the long tentacle fishes continuously through the water.
  • The tentacles are armed with powerful stinging cells, which inject potent venom into prey, immobilising it more or less immediately.
  • Muscles in the tentacle contract and drag prey into range of the digestive polyps.
  • Bluebottles are hermaphrodites, so each individual gonozooid consists of male and female parts. The fertilised egg develops into a planktonic larval form which produces the large blue bottle colony by asexual budding.
  • No fatalities have been confirmed from blue bottles in the Southern Hemisphere, however, there have been several fatalities from the related species (Portuguese man o’ war) in the Northern Hemisphere.
  • Most beachgoers in Australia swim at non-tropical beaches, and so are most likely to come across the more harmless, non-tropical stinger varieties such as the common Bluebottle.
  • For the average person, getting stung by one will present no harmful danger, however, for the very young, elderly, people allergic to them or in extreme cases, they can present further complications.
  • A group of bluebottles is called an ‘armada’, which is the Portuguese and Spanish word for a naval fleet. Large armadas can be found along beaches in Sydney.
  • To us, it hurts, but to a fish, the violence of being impaled by thousands of tiny harpoons and immobilised with a cocktail of muscle toxins and neurotoxins can be powerfully destructive.


Published by Karina Teuma Karina Teuma is a Passionate Marine Biology Enthusiast, Environmentalist, Snorkeller, Freediver, Scuba Diver and more.

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