A mile-long bridge connecting Columbia and Wrightsville will remain dark at night as local officials contend with the annual emergence of millions of mayflies that have swarmed so densely near the bridge’s lights they’ve caused vehicle crashes in previous years.
The bridge blackout is scheduled to begin tonight, and it could continue for weeks as mayflies complete their annual mating ritual in the skies above Veterans Memorial Bridge, which carries Route 462 over the Susquehanna River to link Lancaster and York counties.
That's according to Jake Graham, Columbia Borough's public works manager, who said the bugs’ mating season kicked off sometime overnight. He said he knows because thousands of the dead flies were found beneath the bridge’s lanterns this morning.
“The worst of it was on the Wrightsville side, which is typical,” Graham said, adding that road crew workers used tools to remove them.
The mayflies have been attracted to lights atop the bridge for years, with local officials noting they’ve previously clouded nighttime drivers’ visibility before dying in heaping piles like the ones found Tuesday.
“I’ve seen them a lot worse,” Graham said.
As a solution, municipal officials have, also for years, been turning off the lamps, discouraging the swarms while also leaving the driving surface entirely dark aside from drivers’ headlights.
While alleviating the bridge’s bug problem, the darkened surface presents its own visibility and safety problems for motorists, pedestrians and bicyclists, said Mark Stivers, Columbia Borough manager. Stivers urged nighttime bridge users to use extra caution during mayfly season.
“Our biggest recommendation is, when crossing at night, you should slow down,” he said, addressing drivers.
Still, Stivers said darkening the bridge is, for now, the best solution to the yearly problem.
But it’s likely not the ultimate solution.
In fact, the mayfly swarms were considered during the planning of a multimillion-dollar bridge rehabilitation project proposed by officials at the state Department of Transportation. The proposal includes more than $1 million in lighting upgrades, which planners say should allow the bridge to remain illuminated during mayfly season while also keeping the bugs from its driving surface.
However, project construction isn’t expected to begin until summer 2023, and it’s likely to continue into 2027, a PennDOT official said last month.
In the meantime, it’s likely that lights will continue to be turned off during mayfly breeding season, municipal officials have said.
On Tuesday, both Graham and Stivers said it’s hard to say with certainty how large this year’s mayfly population will be. That’s despite local efforts to make predictions by studying weather, water temperatures and other environmental factors, Stivers said.
“We just can’t find the right recipe to find out exactly when they are going to hatch and how many,” he said.
The same is true for the season’s duration, which Graham said has lasted up to six weeks.