If you want to trap biting flies - use the sticky stuff (Tangle Foot - Tangle Trap Sticky Coating) painted on a blue color .
Learned this from a plant friend. She attached a blue ball (to my eye the ball appeared to be a royal blue color; don't know what color the flies saw it as.) to a hat, painted the blue ball with the sticky stuff, and wore the hat on her head. That put the ball roughly at 6 feet from the ground - according to her research, the ideal height to attract the biting flies such as deer flies.
