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Why do mayflies swarm the Wrightsville Bridge? A new study could answer that soon

Tina Locurto
York Dispatch

A study of mayfly behavior and why the insects are attracted to light produced on the Wrightsville Bridge may prevent future swarms.

Mayflies have had an "unforeseen effect" since 2014, when lighting was installed on the bridge, causing officials to turn off all lighting during the annual mayfly season to prevent large swarms.

The study, contracted by the Pennsylvania Department of Transportation, aims to determine why mayflies are attracted to the bridge’s lights and to formulate solutions that may reduce the number of bugs that swarm the bridge, according to a news release.

Several tests will be conducted during the study, including turning off the majority of lights on the bridge and testing new fixtures with different colors of light.

A swarm of mayflies hovers over the Route 462 bridge over the Susquehanna River late Saturday evening, June 13, 2015, between Columbia and Wrightsville, Pa. Authorities say the swarm was so dense that it caused a series of motorcycle crashes and prompted them to close the bridge. (Blaine Shahan/LNP via AP)

Additionally, floodlight fixtures will be suspended from the edge of the bridge at select locations, to shine light underneath, the release states. 

Testing is scheduled for the following dates:

  • Contractor to temporarily modify light fixtures: June 8 to June 9
  • Data collection of lighting and mayfly interaction: June 10 to June 24
  • Contractor to return light fixtures to original setup: June 25 to June 26

An electrical contractor will perform lighting modifications during the day, causing minor delays for travelers while work is being done. Pedestrians walking along the bridge should also use caution along the sidewalk when passing the contractor's vehicle, the news release states.

— Reach Tina Locurto at tlocurto@yorkdispatch.com or on Twitter at @tina_locurto.

A crew from Lapp Electric retrofit new LED panels into lights along the Columbia-Wrightsville bridge, Tuesday, June 9, 2020. The workers are replacing 8 light panels in different sections of the bridge with a different color light for a study on how to keep millions of mayflies from congregating on the bridge.
John A. Pavoncello photo