We have many species of horse flies in Mississippi although we don't have them all at the same time. Horse flies occur from late March through September with various species occurring at very predictable times of the year. This regularity is caused by their development time and by the fact that they all overwinter as larvae - which sets their clock, so to speak. Horse fly females visit animals only to feed - they do not stay on the animal otherwise. Even then, the fly may complete feeding on the animal before dying.
Horse flies are strong fliers being able to travel miles from their larval habitat.
This also precludes good control programs, as any killed will only be replaced by those flying in from afar. The mouth parts of female horse flies are strong and blade-like. They do not suck blood as most blood feeders, but rather slash a deep and painful cut. They then lap up the flowing blood with a sponge-like mouth part. This biting habit is responsible for the bloody animals when subjected to horse fly attacks.