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How to identify it
- About the size of a house fly, roughly 1/4 inch long; UC Riverside gives 1/4 to 3/8 inch.[2][5][3]
- The giveaway is a stiff, bayonet-like beak (proboscis) that sticks straight out in front of the head. House flies have soft sponging mouthparts that point down and can't break the skin.[1][2][3][5]
- The abdomen has dark spots or blotches in a checkerboard pattern.[2][3][4]
- At rest a stable fly holds its body at an angle, head higher than tail, while a house fly rests flat against the surface.[5]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| House fly | A house fly has sponging, downward-pointing mouthparts and can't bite, lacks the checkerboard abdomen, and rests flat against surfaces instead of head-up.[1][5][2] |
| False stable fly | Despite the name, it doesn't bite: it has sponging mouthparts, is about 3/8 inch long and has a dull reddish mark on the back.[2] |
Where it lives
Found worldwide and mainly a pest of livestock. Weather fronts can carry flies from inland farms as far as 225 km to beaches where they can't establish, and they bite people there; research describes this on the northwestern Florida Gulf Coast and the Lake Superior shore, and Georgia Extension notes flies feeding on beachgoers' ankles along the coast.[6][4][7][3]
Biology and life cycle
Larvae develop in moist, fermenting plant matter rather than fresh manure: hay waste at feeding sites, silage, straw or old manure bedding wetted with urine, spilled feed, grass clippings and compost piles.[1][3][8][5][4]
Females lay their eggs in several batches in that material, and development from egg to adult takes about two to three weeks in summer.[8][3][4]
Both males and females feed on blood, often about once a day. A fly stays on the animal only a few minutes, then rests on a wall, fence or vegetation to digest.[1][8][3][5][4]
Stable flies survive poorly above 86°F, so in hot places numbers peak in mid to late spring and early summer and fall off in midsummer. Georgia says that in the South they may breed all year but are mainly pests in spring and fall.[5][1][3]
Wet years bring more flies: in California, March rainfall predicted how many were biting in late spring and early summer.[5]
In marking studies, half of stable flies moved more than 1.6 km from the farms where they developed, but only 5% went beyond 5.1 km. On northerly winds, though, marked flies have reached northwestern Florida beaches up to 225 km from inland sites within 24 hours, and genetic work points to inland areas northwest of the beaches as the main source.[4][7]
Damage and signs
- On people, the flies go for the legs and especially the ankles, and they can bite through clothing.[2][3][1]
- On dogs they feed around the edges of the ears, leaving the margins scabbed and bleeding; dogs kept in outdoor kennels can be bitten severely on the legs and ear tips.[3][1][2]
- Cattle under attack stamp, switch their tails, bunch together or stand in water, and heavy attacks cut weight gain and milk production. Horses kick and stamp, which can make shoeing hazardous.[3][5][6][8]
Health risk
The bite is painful. Stable flies can carry pathogens on their mouthparts from the blood and skin of one host to the next: a 2013 review lists equine infectious anemia, African swine fever, West Nile and Rift Valley fever viruses as known to be transmitted this way, along with Anaplasma among other bacteria and parasites, and says the hosts involved are mainly livestock and only occasionally people. For ordinary bites, MedlinePlus advises washing the site with soap and water, using ice wrapped in a cloth, and an antihistamine or anti-itch cream if needed; get emergency help for trouble breathing or swelling of the face or mouth.[6][9]
Control
Prevention
For dogs and horses, repellents containing permethrin or pyrethrins help but need reapplying every other day.[1]
Sanitation
Removing breeding sites is the most effective and economical control: clean up wet hay waste, spilled feed and soiled bedding, and spread manure and old bedding thinly so it dries.[1][5][8]
At home, don't leave piles of moist grass clippings. Add them to compost and turn the pile so it heats up and breaks down quickly; a neglected backyard compost pile can supply stable flies to a whole neighborhood.[1][3][2]
Organic bedding such as straw, hay or old manure can produce large numbers of stable flies once animals wet it; on dairies, UC Riverside advises removing it entirely every other week and replacing it.[5]
Traps and physical control
Traps such as Alsynite fiberglass traps can reduce flies in smaller settings such as small dairies, zoo pens or dog kennels, but probably can't control them alone on large operations.[5]
Biological control
Parasitic wasps that attack stable fly pupae are sold for release around livestock. Kentucky calls the approach experimental and unlikely to work where many breeding sites remain, and UC Riverside says releases on large California dairies have not substantially cut fly activity.[10][5]
Pesticides
Fly baits that work on house flies don't control stable flies, because stable flies feed on blood.[8]
Insecticides on resting sites or animals give only temporary relief and are no substitute for removing breeding sites. Flies can develop resistance quickly, so limit residual sprays and rotate chemical classes.[5][8][1]
Where sources disagree
Thorax stripes: UC IPM says stable flies lack the four dark stripes on the thorax that mark house flies, while a 2015 USDA review describes four black stripes, the outer two broken.[1][4]
Eggs: Georgia says a female lays 100 to 400 eggs in her life, Minnesota 400 or more, and the 2015 review 60 to 800; Kentucky gives batches of 40 to 80, and the review clusters of about 20 to 100.[3][2][4][8]
Development time: UC IPM says egg to adult can take as little as 12 days under the best temperatures; Georgia gives 14 to 24 days in warm weather, Kentucky 21 to 25 days in summer, and Minnesota 17 to 50 days depending on food and weather.[1][3][8][2]
Common questions
- Why is a house fly biting my ankles?
- It is probably a stable fly. It looks like a house fly but has a piercing beak and tends to bite people on the legs and ankles, even through clothing.[2][3][1]
- Where do stable flies come from?
- They breed in wet, rotting plant matter such as old hay, grass clippings, compost and soiled bedding. Because they fly well, the source may be some distance away; on beaches, flies can arrive on the wind from farms far inland.[1][3][2][4]
- Do stable flies spread disease to people?
- They are mainly a livestock problem. A 2013 review describes them as mechanical carriers of pathogens in the blood and skin of their hosts, especially livestock and only occasionally people.[6]
Sources
- University of California Statewide IPM Program, “Pest Notes: Flies (Stable Fly section).” ipm.ucanr.edu/home-and-landscape/flies/ (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)
- University of Georgia College of Agricultural and Environmental Sciences, “Compost pile can attract bloodsucking stable flies (N. C. Hinkle, February 16, 2006).” fieldreport.caes.uga.edu/?p=17998 (accessed 2026-11-11)
- International Journal of Insect Science, via PubMed, “Showler and Osbrink (2015), Stable fly, Stomoxys calcitrans (L.), dispersal and governing factors (USDA-ARS).” pubmed.ncbi.nlm.nih.gov/26816486/ (accessed 2026-11-11)
- University of California, Riverside, via VeterinaryEntomology.org, “Stable Fly (Stomoxys calcitrans L.) (A. Gerry, Extension Specialist, University of California, Riverside; September 17, 2012).” www.veterinaryentomology.org/stable-fly (accessed 2026-11-11)
- Parasite, via PubMed, “Baldacchino et al. (2013), Transmission of pathogens by Stomoxys flies (Diptera, Muscidae): a review.” pubmed.ncbi.nlm.nih.gov/23985165/ (accessed 2026-11-11)
- Journal of Medical Entomology, via PubMed, “Jones et al. (1991), Origin of stable flies on west Florida beaches: electrophoretic analysis of dispersal (USDA-ARS).” pubmed.ncbi.nlm.nih.gov/1770514/ (accessed 2026-11-11)
- University of Kentucky Entomology, “ENTFACT-514: Fly Control Around Horse Barns and Stables.” entomology.ca.uky.edu/ef514 (accessed 2026-11-11)
- MedlinePlus, U.S. National Library of Medicine, “Insect bites and stings (Medical Encyclopedia).” medlineplus.gov/ency/article/000033.htm (accessed 2026-11-11)
- University of Kentucky Entomology, “ENTFACT-502: Biological Control of Flies.” entomology.ca.uky.edu/ef502 (accessed 2026-11-11)
- iNaturalist, “Stomoxys calcitrans taxon page (order and family).” www.inaturalist.org/taxa/122223 (accessed 2026-10-06)