Annual mayfly invasion a necessary nuisance

By Tom Venesky tvenesky@timesleader.comSports Reporter

This summer, the area will face an invasion of epic proportion. These invaders will converge by the millions on the Market Street Bridge and other spans across the Susquehanna River. They will create a spectacle, and the occurrence may even temporarily close the bridges.

Per tradition, millions of mayflies will emerge from the river and swarm to the bridges during the summer.

Capt. Donald Crane, of the Wilkes-Barre City Police Department, said insects are more of a problem on the Market Street Bridge than the Veterans Memorial Bridge, and police have to close the span occasionally as a result of the thick swarm.

“The road gets slippery and they get on people’s windshields and you can’t see. It’s not pretty,” Crane said. “It’s like a snow blizzard and, just like snow, it can be a hazard.”

Different types of flies will hatch through the summer. The enormous swarms that are most memorable, covering the Market Street Bridge every summer, are actually white flies (ephron lukeon), a species of mayfly, said Joe Ackourey, co-owner of Dick Ackourey and Sons in Luzerne.

Ackourey, nationally known in fly-tying circles, guesses that the influx will happen on July 24, and he isn’t basing his prediction on a hunch.

“It’s based on water levels and temperatures,” he said. “If it gets cooler or we get high water, the hatch could disperse through August. But right now conditions are right.”

Such hatches are boons to anglers because each triggers a feeding frenzy among just about every fish species in the river, he said. Others feel the swarm is an indicator of a healthier river.

It culminates a process that is under way in the Susquehanna River.

The circle of life

Wilkes University professor Ken Klemow said the white flies are in the nymph stage, going through a series of molts before they emerge as insects. The majority of the insects fluttering around the bridge lights are mostly males, he said. After they mate, the females go back to the river and the males die, thus covering the ground below.

After the nymphs molt into adults, they leave the river and head to the bridges for several reasons.

Michael Dexter, assistant professor of biology at College Misericordia, said the mayflies seek bridges because they have open sky, light and asphalt.

“Dry asphalt reflects polarized light, and it looks like water to the insects and attracts them,” he said. “These mating swarms won’t congregate unless there’s an open sky and a source of light.”

And they won’t congregate in anything less than enormous numbers. Dexter said the transformation from nymph to adult is determined by water temperature, which is one reason why the insects emerge together.

Numbers are important

Another reason is safety in numbers.

“If they all come out at the same time, they overwhelm the predators because they can’t eat them all,” Dexter said.

Klemow said the phenomenon is called numerical response, and for the few days that it lasts it impacts everything from the local environment to traffic.

“It’s nature putting on a show,” he said.

Although mayflies are a native species, the large hatches are something that wasn’t seen on the river decades ago.

“Older people have told me they never experienced this hatch,” said Rick Koval, a naturalist with the North Branch Land Trust.

“When you see a lot of aquatic insects hatching into adulthood, it’s a wonderful indicator of a water ecosystem that’s functional.”

And a river that may be improving, according to Walt Dietz of the Pennsylvania Fish and Boat Commission.

“Mayflies aren’t tolerant of pollution,” Dietz said. “If the water is bad, you won’t see them in significant numbers.”

Tom Venesky, a Times Leader staff writer, may be reached at 829-7230.