Black Fly Pilot Program

Helicopter spraying river for black fly larva Photo courtesy of​

​Why is Maryland treating Washington County for Black Flies?
In response to black fly concerns from citizens in Washington County, Maryland, Governor Larry Hogan has allocated $200,000 for a black fly suppression pilot project (House Bill 870​), directed by Maryland Department of Agriculture (MDA) and Maryland Department of Natural Resources (DNR) in conjunction with University of Maryland Department of Entomology. The pilot black fly treatment and monitoring project will be implemented this Summer (2017) on the Potomac River in Washington County

Planned Treatment Method
Bacillus thuringiensis israelensis (Bti)​​ will be applied by helicopter. While the schedule is subject to change, our preliminary scheduling is for five, monthly applications beginning August 2017. Bti is a naturally occurring soil bacterium that has been demonstrated to be non-toxic to humans, mammals, birds, fish and most invertebrates. Maryland’s program is modeled heavily on Pennsylvania’s program, which has been in effect since the 1980s.

Treatment Areas
Treatment will focus on portions of the Potomac River in Washington County near Williamsport and from Harpers Ferry to Brunswick.​ Map​ 

What product will be used?
The insecticide that will be used for this project is Vectobac 12 AS. The active ingredient is Bti.

Is Bti safe?
The pesticide, Vectobac 12 AS was chosen because of its effectiveness for this use and because it is harmful to a very limited variety of aquatic organisms that only includes midge larvae, black fly larvae, mosquito larvae and a few other aquatic Dipteran (flies) insects. It is not harmful to fish, crabs or other aquatic invertebrates. More Information​

Maryland Department of Natural Resources​ biologists will conduct biomonitoring of aquatic macroinvertebrates and fish in selected streams to ensure there is no impact on the environment and review the effectiveness of the spraying. For more information, email:​.​

Spray Notification​
The Maryland Department of Agriculture will manage the aerial spray contract and issue spray notifications. Click here to sign up for program updates and spray notifications, For more information, email:​
Female black fly taking a blood meal.
Female black fly taking a blood meal (Photo credit: Oklahoma State University)
What are Black flies? 
While black flies are small (2-5 mm length), they can have a big impact on outdoor activities. Some black flies (Diptera: Simuliidae) can impact outdoor recreation and tourism cause serious by their persistent biting and swarming behavior. The black fly life cycle has four stages: egg, larva, pupa, and adult. All are aquatic except the adults, which leave the water to search for food and mates. Larval growth is very temperature dependent, with relatively slow growth during the cold winter months and very rapid growth during warm summer water temperatures. 

The aquatic stages of black flies are often abundant organisms in river ecosystems, where the larvae filter and eat fine food particles from the water column. The immature stages of black flies are aquatic and exclusively inhabit flowing waters. However, black flies are not found in lakes, ponds, swamps, and other standing water habitats. Stream flow is essential for transporting food and oxygen to the immature stages. Black flies can play in important role in local food chains where they are preyed upon by many insect predators, fish, amphibians and birds.​

Tips for Avoiding Black Fly Bites 
  • Avoid areas of high black fly infestation. 
  • Avoid unnecessary outdoor activities at dawn and dusk when black flies are most active. 
  • Wear long pants, long-sleeve shirt and hat when outdoors. 
  • Wear light-colored clothing because black flies are attracted to dark colors. 
  • Use black fly repellents containing DEET. Consult a physician before applying DEET to young children. 
  • Restrict the outdoor play of your children if black flies are present. 
  • Additional personal protection tips​

Human Trafficking GET HELP

National Human Trafficking Hotline - 24/7 Confidential

1-888-373-7888 233733 More Information
on human trafficking in Maryland

Customer Service Promise

The State of Maryland pledges to provide constituents, businesses, customers, and stakeholders with friendly and courteous, timely and responsive, accurate and consistent, accessible and convenient, and truthful and transparent services.

Take Our Survey

Help Stop Fraud in State Government

The Maryland General Assembly’s Office of Legislative Audits operates a toll-free fraud hotline to receive allegations of fraud and/or abuse of State government resources. Information reported to the hotline in the past has helped to eliminate certain fraudulent activities and protect State resources.

More Information