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of the Commonwealth of Pennsylvania

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    ​​​​Welcome to Pennsylvania's Black Fly (Gnat) Suppression Website

    The goal of the Pennsylvania Black Fly Suppression Program is to reduce adult black fly (gnat) populations to tolerable levels during the spring and summer recreational season using environmentally compatible methods. The program involves monitoring and treatment of approximately 1,800 miles of 48 Pennsylvania rivers and streams. DEP biologists and student interns conduct black fly monitoring, laboratory identification of samples, data entry, treatment operations and management of aerial spray contracts. Treatments are done by helicopter or hand applications, using Bacillus thuringiensis israelensis (Bti), a naturally occurring soil bacterium, to selectively target only four black fly species in the Simulium jenningsi species group that bother people. The program currently conducts control work in 37 participating counties with over 6.6 million residents, providing relief from adult black flies so residents and tourists can fully enjoy outdoor recreational activities in Pennsylvania.

    Not sure if it's a black fly? Black flies are often referred to as gnats and are much smaller than the common house fly and closer to the size of a fruit fly. Black flies do not enter buildings or covered areas in any significant numbers. The gnats have the annoying habit of swarming around the heads of people outside on warm days and disrupt outdoor activities. Swatting them is useless as they are quick to return, often flying into people's eyes and sometimes delivering a painful and itchy bite. If you are encountering an issue with black flies (gnats) and would like to report it, you can follow the link and provide additional information.

    If you have any questions or would like more information regarding the PA Black Fly Suppression Program and its operations in Pennsylvania, you can contact the Black Fly Coordinator listed under your county. Any other fly related issues or questions unrelated to black flies (gnats) should be directed to the Penn State Extension Office in your County.

    DEP's Black Fly Suppression Program

    DEP's Black Fly Suppression Program involves aerial and backpack spraying on roughly 1,700 stream miles in 36 counties in the commonwealth. The season runs April 1 through September. 48 rivers and streams spanning more than 1,700 miles are monitored and treated as needed. Spraying activities are performed both by helicopter and ground crews. Prior to any spraying activity, DEP notifies county and local emergency management officials. 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.

    Joining the Program

    1. Citizens report adult black fly (gnat) problems to county personnel or DEP.
    2. County commissioners must submit a written request to join the program to DEP.
    3. Black Fly Suppression Program personnel conduct an extensive one-year countywide survey of black fly larval, pupal and adult populations to determine the need for a control program.
    4. DEP provides results of the survey, data analysis, recommendations, and treatment cost estimates for the county and state, if a control program is recommended in the county.
    5. If county commissioners choose to participate, and adequate funding is available, a county agreement is signed and executed.
    6. DEP water pollution biologists begin monitoring and treating black fly populations the following season under a new or existing aerial application contract.

    Program Funding

    1. State/county cost-sharing of treatment operations, as set forth in county agreement.
    2. All administrative and monitoring costs are paid entirely by DEP, at no cost to the county.
    3. Commonwealth funding for the program is achieved through an annual state budget appropriation.
    4. Counties are invoiced for the local share of the project at the end of each treatment season.​