Don’t swat at your device. It’s the annoying black fly.

The Pennsylvania Department of Environmental Protection (DEP) has begun its black fly spraying program.

In Warren County, the Allegheny River, and Brokenstraw and Conewango creeks will be treated.

“As warmer weather returns, black flies are a pest that can inundate folks seeking outdoor recreation, especially around rivers and streams, DEP Secretary Patrick McDonnell said. “”Using environmentally-compatible methods, this annual initiative reduces this nuisance so that Pennsylvanians and visitors can fully enjoy our natural resources.”

Statewide, more than 1,700 miles of 48 rivers and streams in 35 counties will be treated.

The treatment is specific to the larvae of black flies. “DEP uses Bti, a naturally occurring bacterium, to treat the larval stage of four specific human pest black fly species,” according to a DEP release. “This bacterium degrades quickly in the environment and does not harm the aquatic ecosystem, birds, or other insects.”

Treatments are applied by ground crews with backpacks and from helicopters.

“Prior to any spraying activity, DEP notifies county and local emergency management officials,” DEP said.

“Helicopters can be seen flying over waterways and ground crews using backpack sprayers off bridges and wading in streams conducting control operations on behalf of DEP’s Black Fly Suppression Program.”

“Anyone concerned at the sight of a helicopter or ground personnel is encouraged to call their county emergency management office to verify that a black fly treatment is taking place in their area on that day,” according to DEP.