The flies often move to the animal's belly on extremely hot days or during rain storms. They will fly up in a swarm when disturbed but immediately return to the animal. Both male and female horn flies are blood feeders. Such continual feeding causes the cattle considerable pain and aggravation. Biology, Habits, and Life Cycle Adult horn flies spend their entire lives on cattle.
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.