The adults are 8–12 mm long. Their thorax is gray, with four longitudinal dark lines on the back. The whole body is covered with hair-like projections. The females are slightly larger than the males, and have a much larger space between their red compound eyes. The mass of pupae can range from about 8 to 20 mg under different conditions. Like other 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.
Adult flies have sponging-sucking mouthparts, with which they inject mainly liquid food or food dissolved with regurgitated saliva. Larvae have mouthparts (mandibles) used to tease apart decomposing organic materials. Larvae feed with the ends of the bodies bearing the breathing pores on the surface and their narrow heads imbedded deep in the food source. Just before completing larval development, they leave their food source in search of a dryer place to pupate. This is the time many larval infestations become noticeable. Large numbers of house flies can develop in poultry houses and around barns and feed lots where animal excrement accumulates. House flies developing there can fly to nearby homes and become an nuisance. Around the home, house flies can develop in garbage and piles of fermenting lawn clippings.
I find it at school. It's on my friend's hand. Actually, it stays almost everywhere. Moreover, it's quite fast!