Authorities say a swarm of mayflies was so dense that it caused a series of motorcycle crashes and prompted them to close a Pennsylvania bridge.

The LNP newspaper (http://bit.ly/1SfbVEa ) reports that the mayflies swarmed around the lights on the bridge and then fell to the ground, making piles several inches deep on the roadway.

Police in West Hempfield Township in Lancaster County said the Route 462 bridge between Columbia and Wrightsville was shut down at about 10:30 p.m. Saturday.

Chad Livelsberger, chief of the Wrightsville Fire Company, said three motorcycle crashes occurred because of the flies. There was no immediate word on whether anyone was injured in the accidents.

Officer Brad Rohrbaugh said the bridge was reopened sometime before 6 a.m. Sunday.

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This story has been corrected to revise the number of motorcycle crashes to three from four, based on updated information from authorities.

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Information from: LNP, http://lancasteronline.com