Hordes of mayflies caused crashes and the overnight closure of a bridge in Pennsylvania.

The mayfly swarm reduced visibility, and turned the road surface of the bridge over the Susquehanna River, in Lancaster County, into a treacherous, slippery mess.

Piles of mayflies up to 2ft deep were seen the morning after.

Immature mayflies live in water, before hatching as adults to mate in swarms.

The bridge was closed late on Saturday, June 13, reopening early on Sunday, June 14, police said.

Wrightsville Fire Chief Chad Livelsberger told LancasterOnline: “It was like a blizzard in June, but instead of snow, it was mayflies.

“They were getting in our mouth. We had to close our eyes. We had to swat them away. Even when we got back, it felt like bugs were crawling in you.”