House Flies
Why there are so many flies in your house, how to tell house flies from cluster, blow and small flies, how long house flies live, and whether they bite.
- House fly size
- about 1/4 inch, gray, 4 dark stripes on the thorax
- Lifespan
- about 2–4 weeks as adults
- Egg to adult
- 7–10 days in warm weather
- Breeds in
- garbage, pet waste, manure, compost, dead animals
- Bite?
- house flies no; stable flies and horse flies do
- Health risk
- can carry bacteria from waste to food
Flies in the house almost always mean one of two things: something nearby is breeding them (trash, pet waste, compost, or a dead animal), or they are getting in through a gap you have not found yet. Find which it is and the problem is mostly solved; spraying without that step only buys a day or two.
This page covers the common house fly and its look-alikes, why you suddenly have so many, and how long they live. For the step-by-step plan, go to how to get rid of flies.
What house flies look like
The house fly (Musca domestica) is the most common fly in US homes:
- about 1/4 inch long
- dull gray with four dark stripes on the back of the thorax
- large reddish eyes, clear wings
- spongy mouthparts that dab liquids; they spit on solid food to dissolve it
House flies live wherever people and animals produce waste, from city apartments to farms, and they are worst from June through September.
Types of flies in the house
| Fly | Look | What it means |
|---|---|---|
| House fly | 1/4 in, gray, 4 stripes | breeding in garbage, pet waste, compost nearby |
| Blow fly (bottle fly) | larger, shiny green or blue | a dead animal (mouse, bird) or rotting meat |
| Cluster fly | gray-brown, golden hairs, sluggish | overwintering in attic or walls; not breeding indoors |
| Flesh fly | gray, checkered abdomen | dead animal or meat waste |
| Stable fly | like a house fly but bites ankles | outdoors near hay, grass clippings, livestock |
| Fruit fly | 1/8 in, tan, red eyes | fermenting food |
| Fungus gnat | tiny, black, slender | wet houseplant soil |
| Drain fly | tiny, fuzzy, moth-like | slime in drains |
Why are there so many flies in my house?
Breeding indoors. House fly larvae (maggots) need moist, rotting organic matter for about a week. Check trash cans with loose lids, a forgotten bag in the garage, pet litter or dog waste on a patio, compost, spoiled pet food, and bins where meat scraps sit for days. A sudden burst of 20 or more big, shiny blow flies, often near one room or window, usually means a mouse or other animal died in a wall, attic, or crawl space. The flies will stop on their own in one to three weeks, or sooner if the carcass is removed.
Coming in from outside. Flies follow odors from garbage, grills, and kitchens. Torn screens, doors propped open, gaps around window AC units, and unscreened attic vents all let them in.
Overwintering flies. If slow, clumsy flies show up on sunny windows in fall or on warm days in late winter, they are probably cluster flies that spent the winter inside your walls. They do not breed indoors, so cleaning will not help; sealing will.
How long do house flies live?
An adult house fly lives about two to four weeks. The full cycle from egg to adult takes only 7 to 10 days in summer heat, and a female can lay over 500 eggs. That is why one neglected trash can in July can produce hundreds of flies in two weeks, and why the numbers crash once the source is gone.
Do house flies bite?
No. House flies cannot pierce skin. If a "house fly" bites your ankles, it is a stable fly, which looks similar but has a pointed, forward-facing mouthpart. Horse flies and deer flies also bite. Tiny biting insects are covered in gnat bites.
Are house flies dangerous?
House flies are a real sanitation concern. They move between garbage or feces and food, carrying bacteria on their legs and mouthparts, and are known to spread pathogens such as Salmonella, Shigella and E. coli. Extension guides note they can transmit more than 20 human and animal diseases. In a typical home the risk is low if you cover food and throw out anything flies have been sitting on, but in kitchens, daycares, and near livestock, control matters.
Other "do they fly?" questions
- Carpet beetles: yes, adults fly and come in through windows in spring.
- Crickets: house crickets can fly but rarely do; field and camel crickets mostly jump.
- Earwigs: some species have working wings, but they rarely fly.
How to get rid of flies, in brief
- Find and remove the breeding source: trash, pet waste, compost, dead animal.
- Keep them out: screens, door sweeps, sealed gaps.
- Trap or swat the rest: fly tape, baited traps outdoors, a fly swatter indoors.
Full instructions, including vinegar traps and what products are worth it, are in how to get rid of flies.
House flies in fall and winter
Flies indoors in October through March are rarely house flies breeding inside. They are usually cluster flies, which spend the cold months in attics and wall voids and wander out toward windows on sunny days, or the last house flies that slipped in before the cold. Neither will breed in a heated home without garbage or waste around. Vacuum them up and seal the entry points in late summer the following year.
When to call a pro
Call a pest control company if you cannot find the source after a week, if you suspect a dead animal you cannot reach, or if cluster flies come back every fall (exterior treatment and sealing before they move in works best). Typical one-time fly service runs about $150 to $300 (approximate).
FAQ
Why are there so many flies in my house all of a sudden?
How long do house flies live?
Do house flies bite?
What are the tiny flies in my house?
Can crickets, earwigs or carpet beetles fly?
Sources and real-world experience
This article draws on real stories from forums and reviews, not generic advice. We quote what worked and what didn't.