Helicopters flew low and slow up the Conewango Creek on Tuesday as the state Department of Environmental Protection sprayed for black flies.

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 disrupting 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.

Treatments are done by helicopter or by hand, using Bacillus thuringiensis israelensis (Bti), a naturally occurring soil bacterium, to selectively target only four black fly species that bother people. The program conducts control work in 35 participating counties with more than 6.6 million residents, providing relief from adult black flies so residents and tourists can fully enjoy the outdoors.

Black fly problems parallel improvements in water quality in Pennsylvania. Many large waterways were severely degraded by the beginning of the twentieth century because of unregulated logging, acid-mine drainage, untreated sewage, industry, and urban sprawl. Over the last several decades, many streams and rivers began to show various degrees of recovery, including the return of diverse assemblages of macroinvertebrates and fish. This list included the return of many pollution-sensitive organisms, including the black fly.

Black fly larvae live in fast-flowing waters, feeding on minute particles that are filtered out of the water. They attach to the surface of rocks in rows of black lines. The adults emerge from their aquatic habitat and many species become serious pests of both humans and livestock because of their persistent biting and swarming behavior

The goal of the Pennsylvania Black Fly Suppression Program is to reduce adult black fly numbers to tolerable levels during the summer recreational season using environmentally compatible methods. There are 35 of Pennsylvania’s 69 counties that take advantage of this program, most with extensive creeks and rivers.

The program involves monitoring and treatment of 1,800 miles of 45 Pennsylvania rivers and streams, including the Allegheny River, Brokenstraw Creek and Conewango Creek in Warren County. DEP biologists and student interns conduct black fly monitoring, laboratory identification of samples, data entry, treatment operations and management of aerial spray contracts.

For more information, contact Morgan Thompson at 814-332-6941.