However, satisfactory control has been attained in some states by treating streams with the natural product, Bacillus thuringiensis var. The breeding sites in streams as well as the potential migration from these sites by the adult female black fly limits the use of chemical pesticides to regulate populations. Breeding site treatments have been used in Africa, but generally have not proven effective. Fogging for black flies would have to be done during the day when these insects are actively feeding and when fogging is least effective. These techniques do not seem effective against black flies in the northeastern United States.
Black flies are small enough to pass through window screen or come indoors on or in the hair.
They do, however, prefer to bite out of doors. Long sleeve shirts, long pants and fine screen netting over head help prevent feeding. Coulstons's TM Duranon TM Tick Repellent, a permethrin product designed specifically to repel ticks, also works for black flies as a clothing treatment, but it can only be applied to fabrics, such as hats and shirts, and not to skin. Because black flies feed only during the day, our best advice is to limit your exposure to black flies. If this is not possible, try the available repellents in the hope that one of them will be effective for you in protecting against the black flies bite.