The larvae of this fly also develop in manure. Horse fly and deer fly. The female horse fly and deer fly attack horses. Their bite is extremely painful and causes a flow of blood that attracts house flies. The horse fly is plentiful in Colorado and a real nuisance.
Horse flies carry equine infectious anemia.
The flies lay their eggs in damp or wet soil near streams, irrigation ditches or lakes. Within one week, larvae hatch and emerge later in the season as the full grown adult fly. This tiny, humpbacked fly can congregate in tremendous numbers around horses, causing extreme annoyance and itching. They feed most commonly inside the ear but also are found on the head, neck, chest and abdomen. Their bite can cause hemorrhage and bloody crusts.