faking the flies...

It is a horsefly trap
This is the only proven method that works without putting toxins in the environment The black ball is heated by the sun and thus gives off heat, moving slowly back and forth like a grazing animal, a strong contrast to the background, and also looks to the primitive brain of the horse fly exactly like a tempting prey. Once they sit on the ball they discover that he is deceit, they will fly away up and end up in the pitcher.