We have epidemic horse flies since 3 years of standing water and no crops. Horses fight all day long out on pasture, miles from home, with hundreds covering their bodies. No insecticide works, as horse flies only work by sight. We purchased 4 Epps fly traps, and they DO catch horse flies! You have to clean them out every other day as trays will be full. We collected a full gallon of dead (stinking!) horse flies every other day, a quart at least from each trap. Five gallons of horse flies a week, all summer. But now in 2012, they are the worst ever. So despite the zillions we eliminated, no change for the horses. They can't graze at all during day, walk in circles all day long. Then at night the mosquitoes. Again, the Epps fly traps do work but have not eliminated them for us.