Do something. Feed thru, use parasites from Kunafin in Texas, compost your wet manure, spread your dry manure, put beneficial nematodes under your stall mats, Use Cyonara 9.7% vertical surface spray, create traps using sticky tape, find creative places to put quick bait, use PDZ, Please do something, i hate flies. And, what you do really makes a difference, it sure does for me!  If you would like information about my fly control program see my webpage, http://www.equestriantraining.com/ecology.htm