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Exploring the apperance of Portuguese Man 'O War on First State beaches

Delaware State Parks

This week, DNREC issued warnings to beachgoers after sightings of the venomous Portuguese Man O' War on the Delaware coast. While they look much like jellyfish with their vivid colors and translucent bodies, their stings are far more painful.

Three were spotted on the shores of Cape Henlopen, Fenwick Island and the Delaware Seashore State Park.

Man O’ Wars are usually found further south, in tropical waters, and state officials haven’t seen them for at least 15 years in the First State. So, Delaware Public Media’s science reporter Eli Chen spoke looked into why they’ve made a stop on our shores now.

It would be an understatement to say the Portuguese man of war is a weird creature. It looks like jellyfish, at first glance, with its blue-purple colors and transparent, rubbery appearances, and tentacles that can grow up to 50 feet long.

But unlike jellyfish, each Portuguese man of war isn’t a single organism --  it’s actually made up of several animals that work together to look like one entity. The technical term for this kind of organism is a siphonophore. Sometimes, they’re referred to as the “floating terrors” -- because of their severely painful sting.  

"It’s a nasty, nasty sting. It’s by far the most toxic of our local jellyfish," said Charles Epifanio, a marine scientist at the University of Delaware.


He says stinging creatures that can pack “a wallop” are familiar on the shores of Delaware, between the Lion’s mane and the Chesapeake Bay sea nettle jellyfish.


“The Portuguese man ‘o war is another story,"  Epifanio noted. "We see them here, they’re in our local waters, they occasionally come on our shore. But they’re the varsity.”

If a person is stung, it causes intense pain that lasts for about an hour. That might be joined by headaches, abdominal pain and muscle spasms. It also leaves red welts on the skin that stick around for a couple of days.


“The way stinging works, there are individual cells on the tentacles that have pneumatosis in them, they’re like little harpoons that inject venom. When you disturb the cell, the cell ruptures and the pneumatosis releases the harpoon,” Epifanio explained.

Epifanio says there are a few records of people dying from man o’ war stings, but those are rare instances. Some people may be more sensitive to the stings or potentially allergic to the venom, like with jellyfish. But chances are, he says, you’ll live.

The question on many people’s minds is why the Portuguese man o’ war are here in Delaware, the Jersey Shore, and Long Island. The man o’ wars are usually found in more southern regions, like around Florida. Wayne Kline, Chief of Enforcement for Delaware State Parks, says they haven’t been seen in Delaware for some time.

“We haven’t seen any, at least in Delaware State Park beaches, for a long time. We’re guestimating it’s been 15 years,” said Kline.

Epifanio says he’s definitely seen Portuguese Man O’ War a several times in the last decade near Delaware, but they’re usually found floating well off the coast.

“Offshore fishermen see these things all the time. It’s not particularly uncommon, but the question is how did they get across the continental shelf from the offshore side to the beaches," said Epifanio. "There are some processes that could make that happen.”

For the most part, the Portuguese Man O’ War moves with the wind and tides. It also has a fin that sits on top of the bell part of its body, making the man o’ war look like a strange aquatic taco. And some scientists believe this fin can act like a sail to help it travel.

But otherwise, they drift like plankton, and Epifanio says the most likely theory why the Portuguese man o’war have washed ashore has to do with a concept called downwelling circulation. That’s when the wind blows from the northeast to the south, pushing portions of offshore water onshore.


“And anything in that’s packet of water is going to be deposited on those beaches,” said Epifanio.

Downwelling is a pretty common event, but it’s uncertain how it produced this uncommon appearance of Portuguese man o’ wars. And this gap of knowledge can’t be explained by climate change.


“Waters off of our coast are warming, there’s no doubt of it. The range of organisms from tropical regions is going to extend up to where we are and we’ve seen that with other species," said Epifanio. "But this particular event I don’t think has much to do with climate change.”

Also, we can still count the number of Portuguese Man O’ War we’ve seen off of our fingers. So unless hordes of their companions start to pile on our beaches, it’s best to call this an anomaly.

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