EDGARTOWN (CBS) – Swimmers beware: Portuguese Man O’ War have been spotted on Martha’s Vineyard.

The Edgartown Parks Department posted a Facebook photo of the jellyfish-like sea creature on Thursday, noting there have been reports of them washing up on South Beach.

“Swim with caution,” the department warned.

“While the man o’ war’s sting is rarely deadly to people, it packs a painful punch and causes welts on exposed skin,” the National Ocean Service says.

And be careful about taking a closer look at man o’ war on the beach – experts say they can sting even weeks after washing ashore.