@Arella Mae,
We have a deer fly problem and blow fly, so, whene it gets hot and they start in, we change the pasture cycle for the sheep. We keep the sheep in during the ay and let em graze at night . Horse flies dont like shade and dot feed at night .
ALSO, wheres your nearest pond and swampy stream bank? These flies use wetlands as their larval ground and by cutting the drainage area around steam wetland and ponds, you cut the number of next years flies down.