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This is the Bluebottle or Pacific man-of-war, an animal that is often confused with the By-the-wind sailor we discussed in an earlier Creature Feature. Both animals are blue and when washed up on a beach they can, at first glance, look similar. Let us have a look at the similarities and differences between these two animals.

Firstly, they are both hydroids, not jellyfish and both consist of a colony of polyps living together under a float. In both animals the float or sail is orientated at a slight angle to the body, either to the left or to the right, ensuring that winds will distribute them in different directions.

Supported under the float, both animals have three types of polyps performing specific functions, some catch food, others digest the food, and some are used for reproduction. Both animals have stinging cells on their tentacles to catch and paralyse their prey.

While the two animals share many features, there are ways to tell them apart. The easiest way is to look at float. The Bluebottle gets its name from its transparent bottle-shaped float, which is a muscular polyp filled with gas, unlike the rigid flat disc of chitin of the By-the-wind sailor. The float of the Bluebottle can exceed 15 centimetres in length while the By-the-wind sailor is smaller, around 6-7 centimetres across.

A Bluebottle floating along the surface

The second difference is the size of the tentacles. The By-the-wind sailor has short tentacles around 1centimetre in length, while the Bluebottle’s tentacles can be up to 100 centimetres long. Despite the differences in length both animals use their tentacles to paralyse and hold their prey, then muscles within the tentacles contract drawing the prey up towards the float to be consumed by one of the feeding polyps. Once the meal has been digested the nutrients are shared with all the polyps of the animal. The Bluebottle’s longer tentacles mean it can gather its food, primarily on fish larvae, small crustaceans, and molluscs from deeper below the surface than the By-the-wind sailor.

Their method of reproduction is different too. The By-the-wind sailor is made of either all male or all female polyps while the Bluebottle is a hermaphrodite, with its reproductive tentacles having both male and female parts. Once fertilised the Bluebottle’s egg will join the plankton community and grows by repeated divisions to produce the larger bluebottle colony.

Bluebottle stings can be very painful to humans

First Aid Treatment for Bluebottle sting as follows:

  1. Wash the sting site with seawater and remove any tentacles.
  2. Immerse the sting or run hot water on the skin for 20 minutes. Make sure the hot water will not burn the person. …
  3. If there is no hot water, an ice pack may help to relieve the pain.

Join Sir David Attenborough and watch a relative of the Bluebottle, the larger Portuguese man-of-war as it catches and eats a meal:

If you would like to learn more about the huge diversity of life that can be found along our coasts and shorelines, please contact Education Director Mandy Robertson on for a public event, school holiday program or school incursion/excursion.

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