The Portuguese man o’ war

Portuguese Man o’ War at Palm Beach FL By Volkan Yuksel [CC BY-SA 3.0 (], via Wikimedia Commons
          The jellyfish that isn’t a jellyfish.

The Portuguese man o’ war (or Man-of-War) is an organism that most will identify as being an extremely dangerous, intimidating, and aggressive jellyfish that will seriously harm or kill anyone that comes in contact with its stingers. These are all common misconceptions of this creatures, even down to its identification as a jellyfish. The Portuguese man o’ war is instead what is called a siphonophore, a colonial organism made up of multiple groups of polyps, each with their own specialized role. It is composed of four main parts:

  1. a large, purple, gas filled floatation device called a pneumatophore that lets the organism rest on top of the water and catch prey with its dangling stingers. They can also deflate to briefly submerge themselves.
  2. many digestive polyps called gastrozooids that secrete digestive juices onto caught prey that has been stung and immobilized
  3. tentacles called dactylozooids that can be contracted and retracted
  4. bead-looking polyps on the tentacles that contain specialised stinging cells called nematocysts

These four groups work together successfully to compose a very successful colonial organism.

Another misconception on the Portuguese man o’ war is that they will swim towards you when spotted in the ocean to attack you. This is false because this colonial organism can’t swim; their movement is at the mercy of the ocean currents. The only way it can influence their own movements is by inflating a small crest on the pneumatophore that acts as a sail, catching passing breezes.

One last important misconception to mention is that the sting will kill you. It is often spread that the Portuguese man o’ war is one of the most deadly animals in the ocean and the venom can not only kill fish, but humans too. In reality, while the sting can be excruciatingly painful, it rarely kills. Keeping that in mind, it is advised to avoid this animal anyway if spotted. Even if it has been washed up dead on shore its tentacles can still deliver a painful sting.

In conclusion, the misconceptions surrounding this animal seem to be more prominent than the actual facts. They rarely kill, they aren’t aggressive towards humans, and “it” is actually a “they”.

3 Replies to “The Portuguese man o’ war”

  1. It is amazing how many misconceptions are applied to various species. One of the misconceptions I believed was that the sting of the Man O’ War was capable of killing a human. Has there been any documented cases of human dieing from a sting?

  2. Douglas Ericson says: Reply

    Very informative post! After reading this I was left with the question, How does this colonial organism reproduce? Are there reproductive pieces of each individual zooid that work together to create a new Man O’ War?

  3. Never knew these guys had the ability to inflate and deflate themselves! Do you know the reason they deflate? I’m wondering if they need to be fully submerged to completely rehydrate or for other nutrients in the water.

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