Vineyard beach managers are reporting sightings of Portuguese man-of-wars on south-facing beaches this month, with one report of a person stung.
The jellyfish-like creatures have washed up in Chilmark and Edgartown, with the most reported on Norton Point Beach off Katama.
One Chilmark beachgoer was stung by a man-of-war that washed up on Lucy Vincent Beach in early July, said Karen Pietruska, acting beach superintendent in Chilmark. She said the beach has a first aid protocol for such events, but didn’t elaborate on the incident.
The Trustees of Reservations collected 17 man-of-wars at Norton Point on July 17, as well as one at Long Point Wildlife Refuge in West Tisbury and another at Wasque on Chappaquiddick.
Several have also been spotted at South Beach, in the Katama section of Edgartown. Beach patrols remove the creatures as soon as they are seen, said town parks administrator Marilyn Wortman.
Beachgoers who spot man-of-wars are advised not to touch the creatures, but to alert beach personnel.
“People don’t need to be afraid of them, but just to be aware that they are around,” said Martha’s Vineyard Trustees of Reservations superintendent Christopher Kennedy.
Though similar in appearance to jellyfish, the creatures actually belong to a related phylum: siphonophores. Each man-of-war is made up of multiple mutually benefitting organisms, including a balloon-like compartment that allows the creature to float, and tentacles that hang down into the water.
“They look like a blue balloon when they hit the beach, which attracts the children to them,” Ms. Wortman said.
Man-of-war tentacles can be 10 to 20 feet long, and the balloon-like part is generally 6 to 12 inches in diameter, Mr. Kennedy said. The creatures feed primarily on larval and juvenile fish, stinging their prey to kill it and digesting the nutrients in one of their many stomachs.
They also occasionally sting humans, even after they have washed up on shore. The stings, though painful, are not lethal to humans.
Portuguese man-of-wars typically appear on Vineyard shores in the summer, though their numbers vary. They also washed up in large numbers last year.
The man-of-wars tend to frequent south-facing beaches because they ride in on the Gulf Stream, typically on a southwest wind, Mr. Kennedy said.