If there's one thing mayflies are good at doing, it's dying.

Soon, millions of dead mayflies will be covering the Route 462 bridge in Wrightsville, just as they have in the previous three years. However, local experts are calling this a win for the Susquehanna River and the livability of its habitat.

Good signs: "It's really exciting," said Bill Minarik, executive director of the Lower Susquehanna Riverkeeper Association. "There's been so many people up and down the Susquehanna cleaning the water. At some point, you would hope to see a physical change."

That physical change came about three years ago, Minarik said, when mayflies started to emerge from the river after many years of absence. The nearly inch-long creatures came out of the water for two days, mated and promptly died.

Just one female adult mayfly can lay about 1,000 eggs, said Kris Kuhn, a biologist with the ‎Pennsylvania Fish and Boat Commission. According to Purdue University, more than 175 different species of mayflies exist in Pennsylvania.

Not every egg makes it to adulthood, Kuhn said. This has led to an increase in the number of mayflies hatching every summer, though.

"From a fishery standpoint, the mayfly is a sign of the water quality," Kuhn said. "That's a good sign, seeing these critters coming out of the water. Many fish species feed on them while they emerge from the water and again after they die and land back in the water."

Driving conditions: 

Last year, there was a layer of mayfly carcasses 2 inches thick on the Wrightsville bridge, according to witnesses of the mating events in mid-June. It caused three motorcycle accidents in one night.

"It's just like driving on ice or driving in the snow," Columbia Borough Fire Department Lt. Sean Montgomery said last year. He said the part of the bridge closest to York County got the worst of the flies, for whatever reason.

Motorists driving through such a biblical swarm should treat it much the same way they would an actual blizzard. After all, the cloud of bugs afforded "zero visibility," and their corpses created a thick, slick coating on the ground.

Montgomery also talked about the less-visible annoyance of the mayflies — they stink.

"Like dead fish," Montgomery said.

Celebrating the bug: Even though the bugs might be annoying, Minarik said their appearance is cause for celebration. The Lower Susquehanna Riverkeeper Association is hosting the first Mayfly Festival on Saturday, June 25.

The free event will take place from 10 a.m. to 2 p.m., when the usual biathlon in Wrightsville has in previous years. Registration for the biathlon starts at 8:30 a.m. Minarik said the event will still have the four-mile run and canoe and kayak biathlon.

However, the group hopes to bring light to the hard work so many people have put in to make the river a thriving habitat not only for the mayflies but also for the fish that eat the larvae and the people who swim in the river.

"We're trying to give people a little perspective," Minarik said. "We're hoping people enjoy it."

The Vinegar Creek Constituency will perform at John Wright Restaurant, 234 N. Front St. in Wrightsville. Artisans and crafters will be around the area as well.

For more information on the Mayfly Festival, visit the Facebook event page.

— Reach Katherine Ranzenberger at or on Twitter at @YDKatherine.

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