When I was a kid, it (black fly population) was so bad you couldn't go out of your house. They (black flies) were all over you. Playing ball was terrible; they would be up your nose, in your ears, around your eyes, you would swallow them.
The upper part of the Clarion River was pretty polluted about 15 years ago. It has since been cleaned up and now there's a black fly problem.
About 99 percent of the black flies that fly around your face are females. They act like the mosquito in that they require a blood meal.