A creature nicknamed the "floating terror" and feared for its painful and potentially deadly sting has been showing up on beaches in Nova Scotia.

In the past week, one Portuguese man-of-war has washed up at Crystal Crescent Beach in the Halifax area.

Although they look like jellyfish, Portuguese man-of-wars are composed of a colony of organisms known as a siphonophore. They tend to be found in tropical and subtropical waters but have been known to pop up in Nova Scotia from time to time.

"If it's a really windy, stormy summer," said Bethany Nordstrom, a master's student in biology at Dalhousie University. "They can get blown up north and they have been recorded in Nova Scotia, the Bay of Fundy, the Scotian Shelf several times."

'It's very, very painful'

Nordstrom, who is working on a study of predator-prey dynamics of leatherback sea turtles and jellyfish in Atlantic Canadian waters, said there have been three confirmed sightings of Portuguese man-of-wars in Nova Scotia this summer.

Although the colourful creatures look harmless, beachgoers should be wary of their sting, which can be deadly for some.

"In rare cases they have been known to be fatal when they've stung people but it's usually because somebody has an allergic reaction or doesn't react well to the sting," she said.

"It's very, very painful and the sting can last for a couple of hours but you usually won't die if you come into contact with a Portuguese man-of-war."

'I thought it was a toy'

Amy Clark was at Crystal Crescent Beach last week with her boyfriend and her one-and-a-half-year-old son when she spotted one.

"I thought it was a toy because it was so pretty," said Clark. "It looked like a little bubble, it was floating above the water. That's not something you normally see with the typical jellyfish around here."

When a wave brought it closer, Clark said her boyfriend immediately found a stick and scooted it away from the child.

Amy Clark spotted this Portuguese man-of-war at Crystal Crescent Beach last week. (Amy Clark)

"He said, 'I think that's a man o' war jellyfish,' and I was like 'You've got to be kidding me,' because I've never seen anything like that."

She looked it up online and realized that's exactly what it was.

Clark said her boyfriend was familiar with the creature from travels down south. She said they moved it away from the surf and put rocks over it to prevent any other children from coming into contact with it.

What to do if stung

If stung, Nordstrom recommends rinsing with vinegar and applying heat to the area.

Their tentacles can grow quite long — as much as nine metres on average, she said.

"You really have to be careful if you see one because the small amount you see on the surface does not equal what's under the water."

Nordstrom is asking anyone who spots a Portuguese man-of-war to email a photo and location details to jellyfish@dal.ca.