ST. JOHNS COUNTY, Fla. -- An unusual and painful animal is washing up on local beaches. It looks like fiberglass. It feels like fiberglass, but it's an animal called sea butterflies.

They don't fly, they're not pretty, but these tiny creatures can hurt.

"It gets stuck in your bathing suit and pokes you," Jennifer Janda said. She and her son, Jett, encountered sea butterflies this week in St. Augustine, but they had no idea what it was.

"We went out on the boat," in the Intra-coastal Waterway, "and we got into the water and all of a sudden it was like 'ow, ow, ow!' And I'm thinking maybe its little jellies, and I can't see anything," Jennifer said. "I said, 'I'm getting back in the boat. Something is getting me!'"

Her son Jett said, "Yeah, you could see them. They were white with a little needle."

Those hard-to-see creatures were sea butterflies. They've been spotted along the St. Johns County coastline this summer.

"What we're seeing on the beach is almost certainly their shells," Dan Palmer noted. He is the Curator of Fishes and Invertebrates at Marineland.

Sea butterflies are not insects. "They're mollusks. So they're related to snails and sea slugs," Palmer said. "They have a thin transparent shell."

"They're only on your bathing suit and stick on," Jett Janda said.

His mother said, "They're like straight pins. It's like being stuck with straight pins. It was painful!"

"They don't have venom. There's no stinging to them. They're just sharp," Palmer said.

There is a reason why these sea butterflies wash ashore. "Usually it's from a change in currents or a storm pushing them. Something like that," Palmer said.

According to a marine life expert, the last time sea butterflies appeared in St. Johns County was in 2006.

"It seem like every 5 to 10 years we get them up around here," Palmer said. "And this could be happening more frequently. We've had warmer seas and warmer water."

"They get on the cloth of your bathing suit and you have to take them out carefully," Jett Janda said.

Sea butterflies are something new Janda and her son learned about her home state.

"I grew up here. I've been here for 18 years. I've never seen them before," she shook her head.

And frankly, she hopes to never see them again.