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How to identify it
- Face flies are close relatives of the house fly and look very much like it; only an expert can reliably tell the two apart.[1][3][6]
- Adults are dull gray with four dark stripes on the thorax behind the head.[2]
- Specialists look for a tuft of bristles at the base of the calypter, a small flap just below the wing base.[2]
- Habits give them away: females cluster around cattle eyes, mouths and muzzles on sunny summer days, and in fall the flies gather on sunny south- and west-facing walls of buildings.[4][5][6][2]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| House fly | Nearly identical to look at, but face flies are pasture flies and are not found in feedlots, dry lots or horse stables in summer; indoors they show up mainly in fall, winter and spring on farms and near pastures.[1][4][2] |
| Cluster fly | A bit larger than a house fly, slow-moving, with short golden hairs on the thorax; its larvae develop in earthworms rather than cow manure.[1][6] |
Where it lives
Introduced to North America from Eurasia after World War II and first found in Nova Scotia in 1952, it now occurs across temperate North America wherever livestock or horses are raised; hot summers seem to limit it in the south. Homes most likely to get them are farm homes and houses near pastures where cattle are kept.[3][1]
Biology and life cycle
Females lay eggs only in freshly dropped, undisturbed manure of cattle on pasture or rangeland; Wisconsin says manure less than 15 minutes old. Trampled, urine-soaked feedlot and dairy manure isn't used.[4][5][3][2]
Larvae are yellow and pupate in a white, calcified case.[4][3]
In summer adult females feed on tears, mucus and other secretions around the eyes, nose and mouth of cattle and horses, and on blood and fluid at wounds; males feed on nectar and dung and rest on fences and branches.[4][1][2][3]
Kansas State says there can be as many as 10 generations a year, depending on weather and season length, and as few as three at the northern edge of the range in Canada.[3]
As days shorten in fall, adults stop reproducing and seek shelter in barns, sheds, houses and church steeples, often reusing the same sites each year. On warm winter days they wake and wander into living areas, windowsills and light fixtures.[3][4][2][6]
They are strong fliers: Wisconsin cites a range of about eight miles in five days, and Nebraska says they can travel several miles to find a host.[5][4]
Damage and signs
- Face flies spread the bacterium Moraxella bovis, which causes pinkeye (infectious bovine keratoconjunctivitis) in cattle. The bacteria ride on the flies' mouthparts from eye to eye, and tiny teeth on the mouthparts scratch the eye and open the way for infection.[3][4][7][5]
- Face flies are also intermediate hosts of Thelazia eyeworms of cattle and horses, and a veterinary review lists Musca flies among the carriers.[4][8]
- Feeding annoyance makes cattle bunch up, seek shade or stand in water, cutting grazing, weight gain and milk production.[4][3]
- In homes they are a nuisance only; they don't breed indoors. Once inside walls they are hard to reach, and in uninsulated buildings most die over winter, raining dead flies on whatever is below.[1][6][3]
Health risk
The Kentucky extension entomologist says the clustering flies in homes aren't breeding there and pose no health hazard; Nebraska calls the face fly a non-biting fly. Their medical importance is for livestock, through pinkeye and eyeworms. Human eyeworm infection is rare: in 2018 CDC scientists reported the cattle eyeworm, Thelazia gulosa, in the eye of a woman in Oregon, the first human case for that species and the first human thelaziasis reported in North America in over two decades.[1][3][4][9]
Control
Keep them out
In summer, before the flies move in, seal cracks and openings along eaves, soffits, vents, siding, cable and meter attachments, especially on buildings that had face flies in past years.[2][1][3][6]
Expect sealing to take time; window screens alone won't stop flies that crawl in through small gaps in walls, and Minnesota says caulking alone won't solve the problem.[1][6]
Traps and physical control
Tolerate a few flies in winter and remove them with a fly swatter or vacuum, and search attics and voids for clusters to vacuum up.[2][1][6]
Biological control
On the farm, dung beetles and other manure competitors bury pats before flies can develop; parasitoid wasps sold for house and stable flies don't help against face flies on pasture.[5]
Pesticides
Utah State suggests an insecticidal dust labeled for the site, applied into voids, cracks and crevices where the flies overwinter; Minnesota suggests a permethrin spray on the outside of the building in late summer or early fall.[2][6]
For cattle, Nebraska says forced-use dust bags, oilers and insecticide ear tags give the most effective control, whole-animal sprays need repeating every 10 to 14 days, and feed-through products stop larvae in manure but don't affect adult flies. Treat calves as well as cows, rotate ear tag ingredients between seasons and pull spent tags to slow resistance.[4][5][3]
When to call a professional
Ask your veterinarian about pinkeye treatment and vaccines as soon as one animal shows tearing or squinting.[5][4]
Where sources disagree
Development time: Kansas State says larvae finish in two to three weeks depending on temperature; Nebraska gives about three weeks from egg to adult; Wisconsin says about one month.[3][4][5]
When they move into buildings: Utah State says late August to early September; Nebraska says late September.[2][4]
Pour-on insecticides: Wisconsin says none are specifically labeled for face flies and passing them into manure hasn't been shown to work as a face fly larvicide; Nebraska lists feed-through products, not pour-ons, as the manure-based option.[5][4]
Common questions
- Why do flies show up on my windows in winter?
- Face flies and cluster flies hibernate in walls and attics; warm winter days wake them, and they wander out toward windows and light fixtures.[2][1][4]
- Are face flies breeding in my house?
- No. They develop only in fresh pasture manure and just shelter in buildings, so any you see indoors moved in during late summer or fall.[4][1][6][2]
- Do face flies cause pinkeye in cattle?
- They spread it. The flies carry Moraxella bovis bacteria from eye to eye on their mouthparts, along with irritation from sunlight, dust and grass seed heads.[3][5][7]
Sources
- University of Kentucky Entomology, “ENTFACT-624: Cluster Flies, Face Flies, and Blow Flies in Homes.” entomology.mgcafe.uky.edu/ef624 (accessed 2026-11-11)
- Utah State University Extension, “Face Fly (Nuisance Pests, IPM).” extension.usu.edu/planthealth/ipm/notes_nuisance/face-fly (accessed 2026-11-11)
- Kansas State University Research and Extension, “Face Flies (MF3611).” bookstore.ksre.ksu.edu/pubs/MF3611.pdf (accessed 2026-11-11)
- University of Nebraska-Lincoln Extension, “The Face Fly (G1204).” extensionpubs.unl.edu/publication/g1204/2015/pdf/view/g1204-2015.pdf (accessed 2026-11-11)
- University of Wisconsin-Madison Extension, “Prevent Pinkeye by Controlling Face Flies.” livestock.extension.wisc.edu/articles/prevent-pinkeye-by-controlling-face-flies/ (accessed 2026-11-11)
- University of Minnesota Extension, “Flies.” extension.umn.edu/garden-and-home/home-maintenance/household-insects/flies (accessed 2026-11-11)
- Veterinary Clinics of North America: Food Animal Practice, via PubMed, “The role of environmental factors in the epidemiology of infectious bovine keratoconjunctivitis (Maier et al. 2021).” pubmed.ncbi.nlm.nih.gov/34049661/ (accessed 2026-11-11)
- Animal Health Research Reviews, via PubMed, “Bovine thelaziasis: a re-emerging parasitic disease of cattle and buffaloes (Alemneh and Dagnachew 2025).” pubmed.ncbi.nlm.nih.gov/41398498/ (accessed 2026-11-11)
- American Journal of Tropical Medicine and Hygiene, via PubMed, “Conjunctival infestation with Thelazia gulosa: a novel agent of human thelaziasis in the United States (Bradbury et al. 2018).” pubmed.ncbi.nlm.nih.gov/29436343/ (accessed 2026-11-11)
- iNaturalist, “Musca autumnalis taxon page (order and family).” www.inaturalist.org/taxa/318496 (accessed 2026-11-11)