The housefly (also house fly, house-fly or common housefly), Musca domestica, is the most common of all flies flying in homes, and indeed one of the most widely distributed insects; it is often considered a pest that can carry serious diseases.
The adults are 6–9 mm long. Their thorax is gray, with four longitudinal dark lines on the back. The underside of their abdomen is yellow, and their whole body is covered with hair. The females are slightly larger than the males, and have a much larger space between their red compound eyes.
Like most Diptera (meaning "two-winged"), houseflies have only one pair of wings; the hind pair is reduced to small halteres that aid in flight stability. Characteristically, the media vein (M1+2 or fourth long vein of the wing) shows a sharp upward bend.
Species that appear similar to the housefly include:
The lesser house fly, Fannia canicularis, is somewhat smaller, more slender, and the media vein is straight.
The stable fly, Stomoxys calcitrans, has piercing mouthparts and the media vein is only slightly curved.
