Each year, swarms of mayflies descend on Wrightsville, attracted to convenience stores and other light sources near the river.
Typically, the remains are dispersed around the waterfront.
But with new lights on the Veterans Memorial Bridge, the piles have heaped around the new lanterns closest to the shoreline, sometimes passing for piles of mulch at the base of the lights.
The mayflies typically hatch in late June or early July in the borough, said Wrightsville mayor Neil Habecker, and are prominent in the area for about two weeks each year.
"This has been going on for years," Habecker said. "What's new is the concentration."
Infestation: In the two-week infestation period, Habecker said riding motorcycles over the Veterans Memorial Bridge after dark can be asking for a face full of bugs. Driving a car is bad enough — so many of the insects hit the windshield that it sounds like rain, he said.
Pumping gas at lighted stations is also on Habecker's list of activities to avoid.
"They're that thick that you just won't want to open up your car door," he said.
Inland from the Susquehanna River, Habecker said he hasn't noticed clouds of mayflies any larger than in past years. But near the river and the bridge, with the new lights, the piles of mayfly remains are more noticeable.
"It's almost like you have these small drifts," Habecker said of the sight on the bridge.
PennDOT involvement: The state Department of Transportation found out about the bugs on the bridge when a county manager drove across the bridge last week and noticed what he thought to be spilled mulch, said spokesman Greg Penny.
The manager dispatched a crew to clean up the mess, only to receive a call from a PennDOT employee saying, "It's not mulch. It's dead bugs," according to Penny.
Besides that initial check, Penny said PennDOT won't be involved unless the mayfly accumulations become a safety hazard.
It's one of the "unintended consequences"of the project to install 65 new cast iron 1930s-style lanterns with LED bulbs, Penny said, the $2.1 million federal transportation enhancement grant through PennDOT and led by Columbia borough in Lancaster County.
Brief influx: About 566 species of mayflies can be found across the United States, according to Purdue University's Mayfly Central website.
Mayflies live most of their lives in an immature stage on the water, said Tim Abbey, educator at York County's Penn State Extension. In the adult phase when they can fly, most species live for 1-2 days, though some live for even less than that, he said.
Females return to the water to lay eggs, and then both male and female species die.
For those who aren't used to the insect hoards, Habecker said the bridge and other Wrightsville areas should be free of the mayflies by the beginning of August, if not before.
And though the bugs are largely viewed as a nuisance, they don't bite or transmit diseases, Abbey said. What's more, they're often an indicator of healthy waterways.
"They're sort of a canary in the coal mine," Abbey said, because mayflies tend to be more prominent in areas with less pollutants.
And the large hatch of flies this year is good for the river's ecosystem, too, said Charlie Mills, Hookline and Sinker bait shop owner in York Haven.
Fishermen who catch smallmouth bass in the Susquehanna can't keep them because the population of the species has been so low in recent years. But the bugs are prime meal opportunities for the fish, an indicator that the bass population will have a chance to rebound in the future, Mills said.
— Reach Nikelle Snader at firstname.lastname@example.org.