Females leave only to lay their eggs in manure that is less than two minutes old. Their requirement of such fresh manure results in interesting egg-laying behavior. After mating and feeding, the female horn fly moves to the rear of the animal and awaits defecation. As defecation occurs, the fly heads toward the ground and is blanketed with fresh dung. The life cycle of the horn fly is 3 weeks or more.
Egg laying usually occurs in the early morning.
Each female fly lays up to 500 small, reddish brown eggs in clumps on grass and other vegetation under the manure. Horn fly maggots develop best in grass-type manure from cattle that are on pasture and poorly on the manure from cattle on concentrated feed. Mature horn fly maggots transform to the pupal stage in or below the manure. Upon emergence from the pupal stage, the adult flies immediately seek out cattle to begin feeding. In West Virginia, the horn fly is a pest during warmer months, usually April or May through September or October.