The Pennsylvania Department of Environmental Protection recently began its 2023 Black Fly Suppression Program, which involves aerial and backpack spraying on roughly 1,800 stream miles in 37 counties of the commonwealth.

Local counties include Schuylkill and Lehigh. Carbon and Monroe are not part of the program.

“Pennsylvania is full of beautiful state parks, trails and forests. People across the Commonwealth should be able to enjoy nature without this seasonal pest impeding on their time,” said Rich Negrin, DEP’s acting secretary. “Our black fly suppression program ensures safe and effective treatment of the black fly species.”

According to information from DEP, 48 rivers and streams spanning more than 1,800 miles will be monitored and treated as needed. Spraying activities will be performed by helicopter and ground crews.

The frequency will depend on weather and biological conditions. Treatments cannot occur during periods of heavy rain or when water levels are high because those conditions lower the effectiveness of the treatment and significantly increase the cost of operations.

Before any spraying activity, DEP will notify county and local emergency management officials.

“These treatments are incredibly dependent on the weather, so there is usually only about a day’s notice and even then many get called off or rescheduled due to weather,” said Neil Shader, DEP’s director of communications.

DEP uses Bti, a naturally occurring bacterium, to treat the larval stage of four specific human pest black fly species. It noted that the bacterium degrades quickly and does not harm the aquatic ecosystem, birds or other insects.

During treatment, helicopters fly over waterways and ground crews use backpack sprayers while standing on bridges or wading in streams.

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.