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.
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.
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.