Overview
The house fly (Musca domestica) is the fly almost everyone pictures — the dull grey insect bumping against a summer window or circling the kitchen. It’s the most widespread fly on earth and one of the most consequential, because it lives in close contact with human waste and human food at the same time. House flies breed in manure, garbage, and decaying organic matter, then travel to your counter, your fruit, and your plate, carrying whatever they walked through. For Ontario homeowners the house fly is a warm-weather nuisance; for restaurants and food businesses it’s a health-inspection liability that has to be actively managed. Either way, a persistent house-fly problem is a signal that a breeding source is nearby.
Identification
House flies are 4–7 mm long, dull grey, with four dark lengthwise stripes on the thorax and a slightly hairy body. The eyes are large and reddish, the wings clear, and the mouthparts are sponge-like — there’s no piercing beak. In flight they’re erratic and land constantly. The most-confused look-alike is the stable fly, which is the same size and colour but bites; getting the ID right matters because their sources and risks differ.
| Feature | House Fly | Stable Fly |
|---|---|---|
| Mouthparts | Soft, sponging — can’t bite | Sharp, bayonet-like — bites |
| Bites people | No | Yes, usually around ankles |
| Thorax | Four dark stripes | Four stripes, broader body |
| Abdomen | Grey with dark markings | Checkerboard spots |
| Where you find it | Kitchens, windows, garbage | Near livestock, patios, beaches |
House flies are also confused with the smaller fruit fly — but fruit flies are only about 3 mm, tan-brown, and hover over produce rather than buzzing the windows.
Life Cycle
House flies develop through complete metamorphosis: egg, larva (maggot), pupa, adult. A female lays 350 to 900 eggs over her life, in clusters of 75 to 150 on moist decaying matter. Eggs hatch into creamy-white legless maggots in as little as 8 to 20 hours. The maggots feed and grow through three stages in 3 to 7 days, then form a barrel-shaped puparium that darkens from reddish to black. Adults emerge in anywhere from three days to four weeks depending on temperature. In Ontario’s summer heat the entire egg-to-adult cycle can finish in about a week, which is why a few flies become a swarm so quickly, and why the province sees six or more overlapping generations across a warm season.
Habitat & Behaviour
House flies stay close to their breeding and food sources and rarely travel far when both are available. Outdoors they cluster around garbage, compost, green bins, manure, and pet waste; indoors they rest on walls, ceilings, and window glass, and gravitate to kitchens and garbage areas. They’re active by day and settle at night, often on ceilings and overhead wires. Flies constantly land, taste with their feet, and regurgitate saliva to dissolve food — the behaviour that makes them such efficient carriers of bacteria from filth to food.
Diet
House flies can only consume liquids and solids they can dissolve, using their sponging mouthparts. They feed on almost anything organic: sugars, rotting produce, garbage juices, manure, pet food, meat, and spills. To eat solid food they regurgitate saliva onto it, liquefy it, and sponge it back up — repeatedly depositing gut bacteria onto whatever they land on. Anything sweet, fermenting, or decaying draws them.
Signs of Infestation
- Adult flies indoors, especially clustering on windows and near the kitchen or garbage.
- Small dark specks (“fly spots”) on walls, light fixtures, and window frames — a mix of faeces and regurgitation that signals resting sites.
- Maggots in garbage, green bins, compost, or spilled pet food — a direct sign of an active breeding source.
- A sudden rise in numbers in warm weather, often traceable to a specific bin, drain, or waste source.
Damage Caused
House flies don’t damage the structure of a building. Their impact is contamination: they transfer bacteria and other pathogens from waste to food-contact surfaces. In a commercial setting the “damage” is regulatory and reputational — a fly problem visible during a health inspection can mean a failed report or, for a serious infestation, a closure order, which is why Ontario restaurants run documented pest programs.
Health Risks
House flies are proven mechanical vectors of disease. Because they move between manure, garbage, and food, they can carry organisms including Salmonella, E. coli, Shigella, and others on their bodies and deposit them on surfaces where you prepare and eat food. In a home the risk is a real but manageable sanitation concern. In a restaurant or commercial kitchen it’s a food-safety priority — flies are one of the most common reasons an Ontario food premise fails inspection, and our commercial program treats them as such rather than as a cosmetic nuisance.
Seasonal Activity in Ontario
House flies appear as the weather warms in May, build through the summer, and peak from July through September when heat accelerates their breeding cycle to about a week. Ontario’s warm, humid summers — and the way a heat wave and dry soil push insects toward buildings — concentrate them around homes, patios, and garbage areas. Numbers drop with the first cold nights of fall, and adults die off or become dormant over winter, with survival carried by pupae and any flies sheltering in heated spaces. Rural and semi-rural properties near livestock, and any home with poorly managed green bins, see the heaviest pressure.
Where They Hide
Indoors, house flies rest on ceilings, upper walls, window glass, hanging cords, and light fixtures, and congregate in kitchens and near garbage. Outdoors they cluster on sunlit walls, fences, garbage bins, compost, and any decaying organic matter. Breeding — the part that actually matters — happens in moist waste: green bins, garbage, compost, manure, spilled feed, and neglected drains.
How They Enter Homes
House flies come in through open doors and windows without screens, torn or ill-fitting screens, gaps around doors, and any opening near a garbage or food area. Warm indoor air drawing outward through gaps, plus the scent of food and waste, pulls them toward entrances. Once in, they’re drawn to kitchens, garbage, and windows as they try to get back to light.
Prevention Tips
- Manage waste tightly — sealed garbage and green bins, emptied often, rinsed regularly, and kept away from doors.
- Clean up quickly — wipe spills, cover food, and pick up pet waste promptly.
- Fit and maintain screens on all doors and windows, and add door sweeps.
- Keep drains and floor drains clean so they don’t become a secondary breeding site.
- Store compost properly and turn it; keep it away from entrances.
- Repair torn screens and seal gaps around doors and windows.
- Use sticky traps or an indoor insect light trap to monitor and knock down stragglers.
Most of these take minutes and cut off the breeding sites house flies depend on. For the full-home version, see our DIY pest prevention guide.
DIY vs. Professional Treatment
For a home, house flies are usually a homeowner fix: find and remove the breeding source, seal the entry routes, and knock down the adults. A can of spray isn’t the answer — it kills visible flies while maggots keep developing in the bin or drain you haven’t found. Professional help makes sense when the source is hidden, when numbers stay high despite good sanitation, or for any restaurant or food business, where Ontario law requires documented control and licensed products. Sani IQ identifies the breeding site, treats it, and closes the entry points, backed by our Pest-Free-Or-It’s-Free guarantee. Businesses can compare options on our plans and pricing page or book a commercial assessment.
References
- University of New Hampshire Extension — House Fly Fact Sheet
- Purdue Extension — Filth Flies (House, Blow, Bottle, Soldier and Flesh Flies)
- University of Florida IFAS — House Fly, Musca domestica
Last updated: July 16, 2026 · Reviewed by Sani IQ licensed technicians