The potentially dangerous Portuguese man-of-war have been spotted on beaches around the southern coastline leading to warnings to swimmers to be on their guard.
Irish Water Safety said the creature had been found on shores in Waterford and Cork and may land elsewhere, particularly Kerry.
A spokesman said: “There have been sightings in Tramore, Ardmore, Inchydoney and Schull so far. With a promising weather forecast for the weekend swimmers, surf-ers and families enjoying the beach are at a high risk of encountering them. Other aquatic users will be at a lesser risk and there is a risk that they may drift further north depending on wind direction.”
The man-of-war, which is a siphonophore and not a jellyfish as commonly described, is an invertebrate and carnivore. Its float (the head) can be 30cm long and 12cm wide and its tentacles can reach up to a maximum of 50m.
They can be found in groups of 1,000, floating in warm waters throughout the oceans, most commonly in the tropical and subtropical parts of the Pacific and Indian Oceans and the northern Atlantic Gulf Stream.
“The stinging, venom-filled nematocysts in the tentacles of the Portuguese man-o-war can paralyse small fish and other prey,” the IWS spokesman said.
“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.”
The stings usually cause severe pain to humans, leaving red welts on the skin that normally last two or three days, 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,” IWS said. “A sting may lead to an allergic reaction. There can also be serious effects, including fever, shock, and interference with heart and lung function. Stings may also cause death, although this is extremely rare.
“Medical attention may be necessary, especially if pain persists or is intense, 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 either area becomes red, warm and tender.”
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