Adults are 1/8 to 1/4 inch long, dull gray, with 4 longitudinal black stripes on the thorax Like other filth flies, house flies have sponging mouthparts. They may be easily confused with other similar species. Mature larvae (maggots) are 1/4 to 3/8 inch long, cream colored, without eyes or legs, and tapered at the head end. A dark-colored mouth hook can be seen in the head.

House flies are prolific breeders with as many as 10 to 12 generations in one summer. Adults are attracted to a wide variety of food sources, including fresh food, decaying matter, carcasses, and feces. Eggs are laid in moist areas with larval food and when conditions are right can hatch within 8 hours.

House flies are fast breeders and can become extremely numerous very quickly. Their sponging mouthparts are used to lap up liquid foods, so house flies must regurgitate onto solid foods in order to partially digest the matter. They defecate wherever they land to feed and have been shown to carry more than 100 different disease organisms on their bodies, making them significant transmitters of foodborne and other illnesses. Among the disease organisms carried are those causing salmonellosis, cholera, dysentery, tuberculosis, anthrax, giardiasis, and ascaris infection. In addition, house flies will lay eggs in human and animal wounds, causing a condition known as myiasis. House flies can fly great distances but tend to stay and usually rest close to available food sources.