A scourge of Pennsylvania, the black flies return each year to drive outdoor folks nuts.
This year has been a particularly bad one, according to Bill Andrus, staff member for the Department of Conservation and Natural Resources' black fly suppresson program.
"They are worse this year due to all of the rain that we've experienced which prevented some spray events. Conewango valley is probably the worst region," he said.
"The black fly program is moving along while funding is available. Excessive flows have required several scheduled spray events to be delayed or canceled. The most recent spray in Warren County took place on Wednesday, July 9," he added.
Bacillus thuringiensis subsp. israelensis (Bti) is a naturally occurring soil bacteria used as a microbial insecticide to control the spread of vector-borne diseases, protect public health, and manage insect pest species including black flies and mosquitoes, according to the Pa. Department of Environmental Protection's website.
"Research demonstrated that Bti is nontoxic to humans, mammals, birds, beneficial insects, fish, plants, and most aquatic organisms. Species-specific properties, safety to non-target organisms, rapid breakdown, and reduced insect resistance make Bti an ideal pesticide, with greatly reduced environmental impacts in comparison to man-made chemical insecticides," the website explains.
He explained that adult black flies are strong fliers capable of traveling distances as far as 20 miles from the streams they emerge from. Black flies often congregate at high elevations which could be termed "hotspots."
"I personally have had no luck with repellents but some people claim repellents containing DEET are helpful," he said.
Andrus noted that black flies in Africa are responsible for transmitting a disease called river blindness, however, no human diseases have been linked to black fly species in North America.
The names black fly and gnats are interchangable, according to Doug Orr, the Pa. state-wide coordinator for black fly suppression. He said the clouds, or "ghosts," of insects that surround your head are, in fact black flies.
Because of body morphology, some people are not bitten, and others are bitten so badly the suffer allergic reactions.