True flies are the only insects with two wings. Their other pair of wings have shrunken into drumstick-like organs called halteres. Halteres function as gyroscopes that help flies orient themselves in flight.

Adult houseflies are diurnal and rest at night. If inside a building after dark, they tend to congregate on ceilings, beams, and overhead wires, while out of doors, they crawl into foliage or long grass, or rest in shrubs and trees.