Only thing to do if you live in an area over run by flies is to . . . live somewhere else! Not much help, huh?
I recently moved from Wisconin, home of Mega Millions of Mongo Mosquitoes, to Idaho, where I think I saw a mosquito last fall. Flies have bothered the horses in the corral a bit but I wasn't bothered while riding last fall.
Of course, I haven't ridden through a summer here, yet, so I might be in for a Nasty Awakening. But I hope not!
"Don't just feed it! Ride it!" And the People said "AMEN!"