House flies are 1/8 to ¼-inch long. They are dull gray with four dark stripes on the back of the thorax (segments right behind the head with legs and wings attached). They have two wings; the fourth longitudinal wing vein has a sharp upward turn. The head is dominated by large red-brown compound eyes, which are surrounded by a light gold stripe. Short antennae emerge from between the eyes. They have sponging mouthparts. Mature house fly larvae or maggots are spindle shaped and creamy white. They have dark mouth hooks at the head end and breathing slits that look like a “wavy W” at the larger round tail end. House fly larvae are ¼ to 3/8-inch long when they change to the brown seed-like pupal stage.
Female house flies lay their eggs singly but in clusters of 75 to 150 eggs in a variety of moist, rotting, fermenting, organic matter including animal manure, accumulated grass clippings, garbage, spilled animal feeds, and soil contaminated with any of the above items. A female may lay more than 500 eggs in a lifetime. The eggs hatch within a day, and the young larvae burrow into the breeding medium and complete development in three days to several weeks depending on the temperature and quality of food materials. Larvae migrate to drier portions of the breeding medium to pupate for three days to four weeks before emerging as adults. Under optimum conditions, houseflies can complete their entire life cycles in less than seven days.
The adult flies may migrate to uninfested areas up to 20 miles away, but most stay within one or two miles of the breeding site. Adult houseflies have a general appetite, feeding on foods ranging from excrement to human food. They feed on liquids but can eat some solid foods by liquefying it with regurgitated digestive tract fluids. During the day, houseflies rest less than five feet above the ground and at night they rest above this height. Houseflies have been associated with many filth-related diseases, and, thus, are a significant health concern.