The house fly, Musca domestica, is the most common of all domestic flies, accounting for about 91% of all flies in human habitations, and indeed one of the most widely distributed insects, found all over the world. It is considered a pest that can carry serious diseases. The adults are 1 cm long. Their thorax is gray, with four longitudinal dark lines on the back. The whole body is covered with hair-like projections. The females can be distinguished by being slightly larger than the males, and having a much larger space between their red compound eyes.

Each female house fly can lay approximately 500 eggs in several batches of about 75 to 150. The eggs are white and are about 1.2 mm in length. Within a day, larvae (maggots) hatch from the eggs; they live and feed on (usually dead and decaying) organic material, such as garbage or feces. Their average life cycle is from 14 hours to one week. The maggots then form from larvae to pupae. The adult flies then emerge from the pupae. The adults live from 2 weeks to a month. Having emerged from the pupae, the flies cease to grow; small flies are not necessarily young flies, but are instead the result of getting insufficient food during the larval stage.

Like other Diptera (meaning “two-winged”), house flies have only one pair of wings; the hind pair is reduced to small halteres that aid in flight stability. They are capable of carrying over 100 pathogens, such as those causing typhoid, cholera, salmonellosis, bacillary dysentery, tuberculosis, anthrax, ophthalmia, and parasitic worms. Some strains have become immune to most common insecticides.