Mix Vanilla extract and apple cider vinegar. I'm a skeptic on home remedies, but I got so desperate last year I had to try it. Absolutely worked, if you can get over smelling like vanilla and vinegar. I've never seen the black flies as thick as they were last year in my entire lifetime.

I really hope the cold winter we have had this year knocks a dent in them. It was impossible to fish or hunt where we are. They would fill up your ears, nostrils, and eyes. Killed one of our chickens too, until we started spraying the vinegar/vanilla mix on them every morning.