WESTERLY, R.I. (AP) — A swarm of dragonflies stunned and surprised beachgoers over the weekend in Rhode Island.

Thousands of the dragonflies, relatively large and often beautifully colored insects, descended on Misquamicut beach Saturday. Video of the dragonflies shows beachgoers running for cover and hiding under blankets. People could be heard screaming.

It’s unclear what prompted the cloud of insects to visit the beach for several minutes and then largely disappear.

“One minute everything was calm. The next minute I saw the most dragonflies I’ve ever seen in my l,” Nicole Taylor told WFSB-TV. “It lasted for like 3 minutes, and then they were gone. It was a very strange experience.”

Christina Vangel, who works at Alfie’s Beach Store, said workers had to shoo the dragonflies out. “As the day went on there were tons of them everywhere. We had to close the doors,” she said.

Chris Fiore, whose family owns Alfie’s, across the street from the beach, marveled at the unique onslaught of dragonflies. “It was fascinating. There were big clouds of them,” he said.

The swam of dragonflies also spread across the thousands of concert-goers at the Newport Folk Festival at Fort Adams State Park.

Dragonflies feed mostly on insects like mosquitos and midges, relying on a swiveling head and huge eyes to catch their prey. Some species breed in July and August including the common green darner dragonfly found in Rhode Island. They don’t normally sting or bite humans.

No one quite knows what causes them to swarm, said Virginia “Ginger” Brown, the state’s leading expert on dragonflies on a Zoom call with reporters on Monday. She offered some advice if the rare event ever happens again,

“Enjoy it and observe it, because you might not ever see it again. These are such important insects in the ecosystem, and they are drop-dead gorgeous up close,” Brown said.