Fly Sprays and Wipes for Horses. During hot summer days flies become a nuisance to the well being of our horses. Flies bite and can cause horses to panic. Think about how much you could tolerate while trying to eat (graze). Fly sprays will help. Be sure to spray where the horse cannot reach with their tails. Under the horses belly, the neck, face and the horses back. Turning out in the early morning and late evening also provides some relief from the nasty biting creatures.