Despite its outward appearance, the man-of-war is not a true jellyfish but a siphonophore, which differ from jellyfish in that they are not actually a single creature, but a colonial organism made up of many minute individuals called zooids. Each of these zooids is highly-specialized and, although structurally similar to other solitary animals, are attached to each other and physiologically integrated to the extent that they are incapable of independent survival.
Below the main body dangle long tentacles, which occasionally reach 22 meters (66 ft) in length below the surface, although 10 meters (30 ft) is the average. The long tentacles “fish” continuously through the water and each tentacle bears stinging venom-filled nematocysts (coiled thread-like structures), which sting and kill small sea creatures such as small fish and shrimp. Contractile cells in each tentacle work to drag prey into range of the digestive polyps, the gastrozooids, another type of polyp that surround and digest the food by secreting a full range of enzymes that variously break down proteins, carbohydrates and fats.
In 2010, sightings of the bluebottle were recorded around the small island of Malta in the Mediterranean. In the summer of 2009, Pembrokeshire County Council warned bathers in its waters that the organisms had been sighted in Welsh waters. In Ireland, there were dozens of confirmed sightings (in 2009-2010), from Termonfeckin in County Louth to Ballymoney in County Wexford. On the other side of the Atlantic, they are known to come ashore all along the northern Gulf of Mexico and both east and west coasts of Florida. There is also an abundance of Portuguese Men o’ War in the waters of Costa Rica, especially in March and April, while they are also found off of Guyana. They wash up on the seashore during certain months of the year.
The Portuguese Man o’ War is responsible for up to 10,000 human stings in Australia each summer, particularly on the east coast, with some others occurring off the coast of South Australia and Western Australia.
The stinging venom-filled nematocysts in the tentacles of the Portuguese Man o’ War can paralyze small fish and other prey. Detached tentacles and dead specimens (including those that wash up on shore) can sting just as painfully as the live creature in the water, and may remain potent for hours or even days after the death of the creature or the detachment of the tentacle.
Stings usually cause severe pain to humans, leaving whip-like, red welts on the skin that normally last 2 or 3 days after the initial sting, though the pain should subside after about an hour. However, the venom can travel to the lymph nodes and may cause, depending on the amount of venom, a more intense pain. A sting may lead to an allergic reaction. There can also be serious effects, including fever, shock, and interference with heart and lung action. Stings may also cause death, although this is rare. Medical attention may be necessary, especially where pain persists or is intense, if there is an extreme reaction, the rash worsens, a feeling of overall illness develops, a red streak develops between swollen lymph nodes and the sting, or if either area becomes red, warm and tender.