Summarize this article:

Nontoxic physical traps work best in areas with a lot of livestock, people, or important plants.  Here are some physical trap options that are effective against horse flies:   Light traps. The lights on these traps are especially chosen to attract unwanted insects. When the insect lands on the light, it is either trapped on glue cards or zapped and killed instantly.  Flypaper. This paper contains an adhesive that both attracts and traps house flies and horse flies.  Flies-be-Gone fly trap. This trap holds fly food in a plastic bag for bait. The fly must enter the bag through funnel. Once inside the bag, the fly cannot escape.  Horse Pal fly trap. These large traps have a target specifically designed to attract primarily visual hunters such as horse and deer flies. When the flies approach the target and see that it is not prey, they get trapped in the metal portion of the trap and die from the heat of the sun on the trap. Hang the chair or stool from the ceiling of your shed or other place where horse flies congregate. Attach a dark colored, medium-sized ball to a rope. Attach the rope to the bottom of the chair or stool so that the ball dangles down. Attach Flypaper to the bottom of the chair or stool. Every few hours, start the ball swinging. Because horse flies are attracted to dark color and movement, they will be attracted to the ball. When they fly over and see that it is not interesting, they'll fly upwards and get caught on the paper.

Summary:
Invest in a physical trap. Make your own trap.