Cause
Transmission occurs primarily in the summer months, when the Gasterophilus flies lay their eggs on the haircoat. Within a few days, the eggs hatch and the larvae migrate into the horse's mouth. When a horse licks or chews its haircoat, it stimulates some species of Gasterophilus to hatch. Other species of bots are able to hatch on their own, without stimulation from the horse. After hatching, the bot larvae move into the mouth and are swallowed. Eventually, the bots will travel through the intestinal system and be ejected in a horse's feces.