A recent flurry of Portuguese man o’ war sightings have prompted temporary beach closures in Massachusetts over the past several days after officials spotted the dangerous jellyfish relatives in Yarmouth, Westport, and Chatham.
The Portuguese man o’ war, or Physalia physalis, is a hydrozoan animal named for its likeness to the Portuguese man of war ships. The creature’s balloon-like float and venomous tentacles mean it closely resembles — but technically isn’t — a jellyfish.
Because the animals have poisonous, trailing tentacles that can span several dozen feet, they can harm large portions of an unsuspecting swimmer’s body, according to Peter Gawne, an assistant curator at the New England Aquarium.
The animals are found in locations from New England to Florida to Australia, so it’s difficult to identify specific environments that they thrive in, he said.
Bill Bonnetti, acting director of Natural Resources for the town of Yarmouth, where sightings occurred on Monday, said that weather conditions were ideal for the animals to come ashore over the past several days.
The area has been monitored by staff walking or driving along beaches, as well as by patrol boats in the water, Bonnetti said, adding that he expected to see more of the floating creatures on Tuesday.
“We’ve got these pretty significant southwest winds, warm air temperatures, warm water temperatures, and the incoming tide in concert with the strong southerly winds has been bringing the men o’ war in,” Bonnetti said, pointing to similar weather patterns and sightings in other towns.
Allen Collins, a zoologist at the Smithsonian Institution and director of NOAA’s National Systematics Laboratory, said that while factors like the shape of a coastline can influence the prevalence of the animals washing ashore, wind patterns are the driving factor in bringing them closer.
Still, their presence isn’t new: Man o’ war sightings in the Massachusetts area have occurred since the late 1800s, Collins noted, and the animals are more abundant in warmer months. He said it’s possible that men o’ war are becoming more frequent in northern latitudes, though it’s hard to tell without specific data across time.
“Certainly, as ocean conditions, [namely] climate, changes, then organisms respond in different ways, with some expanding northward,” Collins said. “This is plausible for Physalia, but I am not aware of specific studies that show this.”
In Yarmouth, officials closed beaches Monday after receiving multiple reports that men o’ war had washed ashore.
Westport’s Horseneck Beach State Reservation closed Sunday beginning at 6 p.m. in response to Portuguese men o’ war and an “intense rip tide,” officials posted to social media.
And in Chatham, Harding’s Beach has faced closures for the past several days after officials first reported Saturday that “a number of Man O’War came ashore.” The animals were also spotted at the town’s Ridgevale Beach Sunday, prompting guidance for visitors to adhere to “No Swimming” postings and lifeguard instructions.
Experts and officials alike said the best way for beachgoers to stay safe in areas where the animals have been spotted is to wear a protective layer in the water or stay out of the water altogether.
Tentacle ensnarement can yield a range of injuries, from mildly painful stings to serious complications, Collins said.
Victims should rinse affected areas with undiluted vinegar and hot water and remove any lingering tentacles from the skin as soon as possible. Contrary to popular belief, Collins said, urine “does nothing to help.”
Anjali Huynh was a Globe intern in 2022.Follow her on Twitter @anjalihuynh.