Most horse owners have peered inside their horse’s ear to find what looks like an accumulation of fungus-like growths.  The presence of this material seems to irritate owners far more than the horse itself.  These growths are in fact aural plaques and are caused by a hypersensitivity to the bites of the tiny black flies one finds in and around the ears, or under the horse’s belly where it can cause swelling and dermatitis.  The best advice is to leave them well alone; medications within the ear canal can do much more harm than good.  If your horse is especially worried by flies, the best advice is to apply fly repellants around the outside of the ear and head, or to fit a hood which has ear pieces. 

Changing the times the horse is turned out to pasture, by avoiding the mornings and evenings when the flies are most abundant, can also be helpful.