PennDOT calls it an “unintended consequence.”

Columbia’s mayor thinks it’s simply a nuisance river towns have to learn to live with.

But when Modie Mowrer drove across the Veterans Memorial Bridge between Columbia and Wrightsville a couple weeks ago, she experienced what she still calls “a nightmare.”

“Oh my gosh, it sounded like a hail storm,” she recalls. “I could see the guts on my windshield. I didn’t know what it was,” said the 26-year-old woman who works in Marietta.

What it was — and still is — are thousands and thousands of mayflies hatching from the Susquehanna River below and gravitating en masse to the bridge’s new Art Deco lights, just installed last month as part of a $2.1 million renovation project.

The intensity of the swarms amazed even those who have long lived along the river and are used to such phenomena.

To the uninitiated, though, a blizzard of bugs can be unnerving as they splatter against your windshield and blow across the road in front of your car.

Mowrer’s parents were panicked the first time they drove across the Route 462 bridge at night a couple weeks ago.

“They said they didn’t know what to do,” she says. “They just slowed down.”

Mowrer says that despite repeated washings, she still hasn’t been able to get all the bugs off her car. And her visits to her parents in Columbia end before it’s dark.

She says she saw a motorcyclist put a bandanna across his face when crossing the bridge.

PennDOT became aware of the situation a week ago when a supervisor who lives in York County was crossing the bridge to go to work at PennDOT’s Lancaster office.

He arrived at work and sent a clean-up crew to the bridge, instructing them to clean up mulch that had spilled from a truck.

Only, when the crew arrived, they found themselves removing not mulch but the desiccated shells of thousands of bugs.

“One of the crew members said it was like driving through a snowstorm,” according to PennDOT’s Greg Penny.

The dead bugs have filled the platforms holding the lights to overflowing, and tumbled like lava onto the columns, sidewalks and roadway.

The bugs are mainly flocking to the lights nearest the shoreline on both the Columbia and Wrightsville sides of the bridge.

For years, the bridge has been lit by lights on long poles well above the decking. But the new lights, placed on where they were when the bridge opened in 1930, are only about 10 feet above the road surface.

That’s like a magnet for emerging mayflies.

“They mate in large clouds, often above the water they emerged from, and often near light sources,” notes Blanton Amspacher of Dominion Pest Control.

“Once they mate, the males die promptly while the females lay their eggs and then also die. The insects on the bridge lamps are likely post-mated that died from exhaustion. The adult form does not feed or sting and is completely harmless.”

Amspacher says there are more than 300 very similar looking species of mayflies in Pennsylvania. They vary in size but most don’t get over an inch and a half.

The mayfly blitz is such a fixture in Harrisburg each summer that as an April Fool’s Day joke this year, the Harrisburg Senators baseball team, which plays on an island in the river, sent out a bogus press release announcing the team was changing its name to the Harrisburg Mayflies.

Columbia Mayor Leo Lutz says maintenance crews have used leaf blowers to clean the bridge in the last two weeks.

PennDOT's Penny says the agency would keep an eye on the situation but so far it has not posed a safety issue.

“If it becomes a persistent problem, we may have to do some creative thinking to deal with it.”

The effort to restore the lights to their original appearance was a long effort headed by Rivertownes PA USA., a nonprofit group.

Residents of Columbia are ecstatic about the historically correct new appearance of the bridge, according to Lutz. Even boaters love them because now they can see rocks in the river while fishing at night.

The appearance of the mayflies is an encouraging sight as they are one sign of an improving Susquehanna, he adds.

“It’s a nuisance, I guess you could say, but it’s something we’ve learned to live with over the years. That’s one of the things of living along the river.”

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Ad Crable is a Lancaster Newspapers staff writer and outdoors columnist who covers the environment and nuclear energy. He can be reached at or (717) 481-6029. You can also follow @AdCrable on Twitter.