Campers and fishermen are not the only sufferers. Forest and farm animals are afflicted as well. In years of bad outbreaks Saskatchewan cattlemen lose millions of dollars as their cows suffer weight loss, sicken and even die, suffocating on thousands of the attacking insects they can t help but inhale. Another blackfly species attacks only loons and I have seen the poor birds clothed in them. No wonder these divers stay under water so long.
Some blackflies are disease vectors.
One spreads malaria-like leucocytozoa among birds. Far worse, African and Latin American blackflies carry onchocerciasis, a terrifying human plague also known as river blindness. In some areas almost a third of adult males are blinded. We are, however, no longer entirely defenseless against this scourge. Deet and permethrin enhanced sprays offer better, but far from complete, protection.