Adults are gray to black, with four dark, longitudinal lines on the thorax, slightly hairy bodies, and a single pair of membranous wings.

They can carry pathogens on their bodies and in their feces, contaminate food, and contribute to the transfer of food-borne illnesses, while, in numbers, they can be physically annoying.

Houseflies, with short life cycles and ease with which they can be maintained, have been found useful for laboratory research into aging and sex determination.

Authors sometimes choose the housefly to speak of the brevity of life, as in William Blake's 1794 poem "The Fly", which deals with mortality subject to uncontrollable circumstances.

[11] At the end of each leg is a pair of claws, and below them are two adhesive pads, pulvilli, enabling the housefly to walk up smooth walls and ceilings using Van der Waals forces.

[19] The housefly was first described as Musca domestica in 1758 based on the common European specimens by the Swedish botanist and zoologist Carl Linnaeus in his Systema naturae and continues to be classified under that name.

The eggs are white and are about 1.2 mm (1⁄16 in) in length, and they are deposited by the fly in a suitable place, usually dead and decaying organic matter, such as food waste, carrion, or feces.

The larvae avoid light; the interiors of heaps of animal manure provide nutrient-rich sites and ideal growing conditions, warm, moist, and dark.

The male then reverses onto her abdomen and the female pushes her ovipositor into his genital opening; copulation, with sperm transfer, lasts for several minutes.

In general, fresh swine and chicken manures present the best conditions for the developing larvae, reducing the larval period and increasing the size of the pupae.

Adults are mainly carnivorous; their primary food is animal matter, carrion, and feces, but they also consume milk, sugary substances, and rotting fruit and vegetables.

[14] In cooler climates, some houseflies hibernate in winter, choosing to do so in cracks and crevices, gaps in woodwork, and the folds of curtains.

[28] Houseflies sometimes carry phoretic (nonparasitic) passengers, including mites such as Macrocheles muscaedomesticae[29] and the pseudoscorpion Lamprochernes chyzeri.

[37][38] Houseflies can fly for several kilometers from their breeding places,[39] carrying a wide variety of organisms on their hairs, mouthparts, vomitus, and feces.

Parasites carried include cysts of protozoa, e.g. Entamoeba histolytica and Giardia lamblia and eggs of helminths; e.g., Ascaris lumbricoides, Trichuris trichiura, Hymenolepis nana, and Enterobius vermicularis.

[40] Houseflies do not serve as a secondary host or act as a reservoir of any bacteria of medical or veterinary importance, but they do serve as mechanical vectors to over 100 pathogens, such as those causing typhoid, cholera, salmonellosis,[41] bacillary dysentery,[42] tuberculosis, anthrax, ophthalmia,[43] and pyogenic cocci, making them especially problematic in hospitals and during outbreaks of certain diseases.

[40] Disease-causing organisms on the outer surface of the housefly may survive for a few hours, but those in the crop or gut can be viable for several days.

[47] In China, Mao Zedong's Four Pests Campaign between 1958 and 1962 exhorted the people to catch and kill houseflies, along with rats, mosquitoes, and sparrows.

The Baoshan bombing produced epidemics that killed 60,000 people in the initial stages, reaching a radius of 200 kilometres (120 mi) which finally took a toll of 200,000 victims.

[49] The ability of housefly larvae to feed and develop in a wide range of decaying organic matter is important for recycling of nutrients in nature.

[50] Housefly larvae can be mass-reared in a controlled manner in animal manure, reducing the bulk of waste and minimizing environmental risks of its disposal.

Physical controls include screening with small mesh or the use of vertical strips of plastic or strings of beads in doorways to prevent entry of houseflies into buildings.

Fans to create air movement or air barriers in doorways can deter houseflies from entering, and food premises often use fly-killing devices; sticky fly papers hanging from the ceiling are effective,[44] but electric "bug zappers" should not be used directly above food-handling areas because of scattering of contaminated insect parts.

Keeping garbage in lidded containers and collecting it regularly and frequently, prevents any eggs laid from developing into adults.

Unhygienic rubbish tips are a prime housefly-breeding site, but if garbage is covered by a layer of soil, preferably daily, this can be avoided.

Resistance monitoring is vital to avoid continued use of ineffective active ingredients such as found in the notably severe example of Freeman et al 2019 in Kansas and Maryland, USA.

These include the introduction of another species, the black soldier fly (Hermetia illucens), whose larvae compete with those of the housefly for resources.

[15]: 96  Because the somatic tissue of the housefly consists of long-lived postmitotic cells, it can be used as an informative model system for understanding cumulative age-related cellular alterations.

Although a wide variety of sex-determination mechanisms exists in nature (e.g. male and female heterogamy, haplodiploidy, environmental factors), the way sex is determined is usually fixed within a species.

[72][73][74] William Blake's 1794 poem "The Fly", part of his collection Songs of Experience, deals with the insect's mortality, subject to uncontrollable circumstances, just like humans.