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How to identify it
- Adults are dull gray, about 1/6 to 1/4 inch long (under 3/8 inch), with four dark stripes running down the back of the thorax. Clemson puts adults at about 1/4 inch long.[1][2][4]
- Sponging, non-biting mouthparts; the fly liquefies solid food with saliva or regurgitated fluid, then sucks it up.[1][2]
- Larvae (maggots) are cream colored, blunt at the rear and tapered to a point at the head.[1]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Stable fly | Looks similar but has a checkerboard pattern on the abdomen and a bayonet-like mouthpart; it bites people and animals. UC adds that stable flies lack the house fly's four dark stripes on the thorax.[2][1] |
| Little house fly | Smaller (1/8 to 3/16 inch) and more slender; males hover in rooms for long periods. It is most common in cooler spring and fall weather. UC says it tends to hover at face height and rarely lands on human food.[2][1] |
| Cluster fly | A little larger, with golden hairs on the thorax, and shows up indoors in fall and on warm winter days rather than breeding indoors.[2][3] |
Where it lives
Found throughout the world. Eggs are laid in warm, moist organic material such as garbage, manure, lawn clippings, rotting fruit and vegetables, and soil contaminated with them; flies indoors have almost always come in from outside.[1][2]
Biology and life cycle
Egg counts differ by source: UC says each female lays several batches of about 100 to 150 eggs, Minnesota gives batches of 75 to 100, and Clemson says a female can lay up to 900 eggs. Minnesota says females live three or four weeks.[1][2][4]
In warm summer weather, development from egg to adult can take as little as 7 days. Clemson gives as little as six days.[1][4]
Older larvae leave the breeding material to pupate in drier, cooler spots.[1]
House flies are strong fliers and can travel up to 20 miles, though most stay within about two miles of where they bred.[2]
Clemson groups the house fly with the outdoor breeders: if many are inside, the breeding site is probably indoors or near an open vent, window or door.[4]
Damage and signs
Health risk
House flies are mechanical carriers of germs. A 2018 systematic review of 99 studies found more than 130 pathogens on house flies, mostly bacteria, including some serious and life-threatening species and antimicrobial-resistant bacteria and fungi; most of the flies were caught in or around homes and animal farms, and the germs were usually on the flies' body surfaces. A 2022 review of 78 studies tracked E. coli, Enterococcus faecium, Klebsiella pneumoniae, Pseudomonas aeruginosa and Staphylococcus aureus on house flies worldwide.[5][6]
Control
Keep them out
Keep screens in good repair (14- to 16-mesh) and seal cracks around doors and windows; this is the first line of defense. Clemson also lists vents among the openings to keep screened.[1][2][4]
Sanitation
Remove garbage, pet feces and rotting fruit at least weekly, bag trash and use cans with tight lids placed as far from doors as practical, and cover compost; poor sanitation and exclusion are the main causes of fly problems. Clemson says that if you see many house flies, look for fresh animal feces or uncovered garbage cans first.[1][2][4]
Traps and physical control
Use a swatter or sticky fly ribbons for a few flies indoors, and baited cone traps outdoors away from the house. Don't use bug zappers or swatters near food preparation, since fly parts can scatter onto food.[1][2]
Pesticides
Insecticides are a last resort and won't give long-term control; house flies are resistant to many of them. Indoors, a non-residual pyrethrin aerosol can knock down flies; fly baits in trash areas help only if sanitation is also handled. Clemson says sprays shouldn't be needed once breeding sites are gone, since adults don't live long; an aerosol is only for excessive numbers after the source is removed. Minnesota likewise calls a flying-insect aerosol a short-term fix.[1][2][4]
When to call a professional
If large numbers keep showing up after you have cleaned up, Clemson says a breeding site was probably missed: check chimneys, attics, crawl spaces, vents, under floorboards and above ceiling tiles, and consider a professional for infestations that sanitation doesn't fix.[4]
Where sources disagree
Eggs: about 100 to 150 per batch (UC), 75 to 100 per batch (Minnesota) or up to 900 per female (Clemson). Development: as little as 7 days in summer heat (UC) or six days (Clemson). Size: 1/6 to 1/4 inch (Minnesota), about 1/4 inch (Clemson) or under 3/8 inch (UC).[1][2][4]
Common questions
- Do house flies bite?
- No. Their sponging mouthparts can't bite; the biting look-alike is the stable fly.[1][2]
- How fast do house flies breed?
- In summer heat they can go from egg to adult in about a week (as little as 7 days per UC, six per Clemson), and each female lays several batches of eggs, about 100 to 150 per batch according to UC or 75 to 100 according to Minnesota.[1][4][2]
- Can house flies make you sick?
- They can carry germs onto food. Systematic reviews have found more than 130 pathogens on house flies, mostly bacteria such as E. coli and Staphylococcus aureus, including drug-resistant strains.[5][6]
Sources
- University of California Statewide IPM Program, “Pest Notes: Flies, Publication 7457 (April 2015).” ipm.ucanr.edu/legacy_assets/PDF/PESTNOTES/pnflies.pdf (accessed 2026-11-11)
- University of Minnesota Extension, “Flies (reviewed 2024).” extension.umn.edu/garden-and-home/home-maintenance/household-insects/flies (accessed 2026-11-11)
- Penn State Extension, “Cluster Flies.” extension.psu.edu/cluster-flies (accessed 2026-11-11)
- Clemson Cooperative Extension, Home & Garden Information Center, “Nuisance Flies.” hgic.clemson.edu/factsheet/nuisance-flies/ (accessed 2026-11-11)
- BMC Public Health, via PubMed, “Khamesipour et al. (2018), A systematic review of human pathogens carried by the housefly (Musca domestica L.), BMC Public Health 18:1049.” pubmed.ncbi.nlm.nih.gov/30134910/ (accessed 2026-11-11)
- Veterinary Medicine and Science, via PubMed, “Monyama et al. (2022), Bacterial pathogens identified from houseflies in different human and animal settings: a systematic review and meta-analysis.” pubmed.ncbi.nlm.nih.gov/33955703/ (accessed 2026-11-11)
- iNaturalist, “Musca domestica taxon page (order and family).” www.inaturalist.org/taxa/120156 (accessed 2026-11-11)