As warmer weather returns, so do black flies - a pest that can inundate folks seeking outdoor recreation, especially around rivers and streams. Also known as gnats or buffalo gnats, black fly populations have increased in the past few decades as the rivers, lakes, and streams where they breed have gotten cleaner.
So, while it's good news that our waterways have improved, it also means an uptick in flies, which can be a nuisance when you're trying to enjoy the outdoors. Fortunately, the Department of Environmental Protection is taking steps to control black flies in a safe and effective way through its annual
Black Fly Suppression Program. This year, DEP will be working along 1,700 miles of
48 rivers and streams in 35 participating counties, and operations will occur once every 10 to 15 days until funding is exhausted.
The program is open to any county that requests the program. Counties typically request this based on residents' complaints, so if you have a black fly problem in your area, contact your county or submit an
online complaint to the DEP.
Black fly spraying first started in 1983 along the Susquehanna River in Dauphin County in response to several years of citizen complaints in the Harrisburg area; in fact, a group of Harrisburg citizens formed a group called "Neighbors Against Gnats."
DEP uses Bti, a naturally occurring bacterium, to treat the pests in their larval stage. Bti is not only effective at controlling black flies, it's also not harmful to the environment. It degrades quickly and does not harm the aquatic ecosystem, birds, or other insects. It's also not harmful to humans. If you come in contact with it, simply wash with soap and water.
The spraying takes place in the air and on the ground, so keep an eye out for a spray operation if you're on or near a waterway. The helicopter pilots that treat the larger streams and rivers watch for boaters, tubers, and anyone fishing and adjust where they spray when they see people. If you see a low flying helicopter, just make yourself visible so the pilot can see you and move the spray site. If you see a backpack spray operation, just stay a reasonable distance from the biologists and allow them to work.
Unfortunately, black flies are just a part of summer, but DEP is working across the state to ensure that they're not a total buzzkill during your outdoor activities.
For more information on Pennsylvania's Black Fly Suppression Program, visit