The battle against flies is constant, but there are ways to reduce these costly and irritating pests — without toxic chemicals. There are several types of pest flies, with different habits and behavior, so a combination of tactics is usually most effective when trying to eliminate or reduce flies. House flies and stable flies (the latter are aggressive biters, tormenting horses and cattle) breed in manure and rotting organic matter such as old hay and bedding. Horse flies and deer flies breed in swampy areas and black flies breed in flowing water.

Flies are the most common and troublesome external parasites of horses. During the warmer months of the year no region is free of these pests. Flies cause much irritation, and can also spread disease. Large numbers can result in excessive blood loss. Fly bites can also result in skin allergies due to hypersensitivity reactions. The annoyance from flies can disrupt grazing; horses may run frantically to get away from biting flies, or seek out shady areas to swish and stomp. Flies can also distract a horse when you are riding or working with him; he may pay more attention to flies than he does to you.