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How to identify it
- Adults average about 1/8 inch long, tan to dark brown, black or yellowish, with a pronounced hump behind a small head. NC State gives a range of 2/64 to 1/4 inch for the group.[1][2][4]
- The wings have heavy dark veins along the front edge, while three or four veins across the middle run almost parallel with no linking cross veins.[2][3][4]
- Watch how they move: phorid flies run quickly across a surface in short bursts before taking off, which is why they're called scuttle flies. Their long, flattened hind legs help them run.[2][3][4]
- Pupae are oval, slightly flattened cases with short spikes and two breathing horns, and they may coat surfaces near where the larvae fed.[4]
Look-alikes
| Look-alike | How to tell them apart |
|---|---|
| Fruit fly | Fruit flies have a larger head with red eyes and stay near fermenting food. Phorid flies have brown eyes, a humped back and long hind legs, and spread more widely through a building.[1][4] |
| Drain fly | Drain flies are fuzzy and moth-like, with broad hairy wings held flat or roof-like over the body, and they fly only a few feet at a time.[2] |
Where it lives
Megaselia scalaris is a very common fly found worldwide, and phorid flies show up in homes and, even more often, in commercial buildings.[1][2]
Biology and life cycle
NC State names Megaselia scalaris and Dohrniphora cornuta as the two most common phorid flies in and around homes.[4]
Larvae feed on a huge range of moist, decaying plant and animal matter, from garbage, dung and carcasses to wet potted-plant soil, dirty mop heads, compost and broken garbage disposals. A review of Megaselia scalaris describes its larval diet as unusually broad.[2][1][4][5]
A common indoor food source is the film of moist organic matter that builds up inside drains and plumbing.[1][4]
Development is fast, so numbers can jump suddenly even when only a few flies got in at first. Each female lays her eggs in batches on or beside the food source.[4][1][2]
Phorid flies can burrow through soil to reach buried food; Texas A&M says through six feet or more to reach caskets, which earned them the name coffin flies.[2][3][4]
Adults are active and may travel far from the breeding site, which is one reason the source can be hard to find.[1][3][4]
Damage and signs
- A few indoors isn't unusual, but large numbers usually point to an unsanitary breeding site somewhere in or under the building.[2]
- Soil soaked by a leaking sewer line under a building can produce severe indoor infestations. Fixing it may mean opening the slab, repairing the pipe and removing all the contaminated soil.[2][4]
- Because they breed in sewage and decaying matter, phorid flies are an especially unwelcome sanitation problem in kitchens, food plants, hospitals and morgues.[4][2][3]
Health risk
Megaselia scalaris larvae occasionally infest people, a condition called myiasis. Published case reports describe larvae in a leg wound of a hospitalized patient in Kuwait, in the urine of a patient with transverse myelitis in India, and in the urine of an Iranian man with urinary tract problems who had traveled to Thailand. Each case involved a person who was already ill or injured.[6][7][8]
Control
Keep them out
When breeding material in a crawl space can't be removed, dry the area thoroughly and caulk the openings flies use to reach living areas.[1]
Sanitation
Finding and removing the breeding material is the only lasting fix; if moist decaying matter is removed or dries out completely, the flies can't breed.[1][3][4]
Start the search in the kitchen with stored potatoes, onions and other food, then check garbage cans, drains, leaking appliances such as refrigerators and washing machines, crawl spaces and wall voids.[4][3]
For drains, scrub the pipes or use drain cleaners made to remove organic residue; foaming products can reach pockets that poured liquids flow past.[1][4][2]
Hot water and bleach are unlikely to clear the debris phorid flies breed in. NC State adds that bleach and strong cleaners shouldn't be poured down drains at all, because they can react dangerously with other compounds in the lines.[1][4][2]
Traps and physical control
Pinpoint the source with sticky traps placed around the building to see where flies concentrate. A trap sticky side down just above a sink drain, or tape or a clear bowl over a drain, shows whether flies are coming up from it.[1][3][4]
Pesticides
Spraying adult flies doesn't solve the problem, because new flies keep emerging from the breeding site.[1][3][4]
When to call a professional
If no source turns up, NC State suggests having a plumber check the drain lines with a flexible scope or smoke test for breaks.[4]
If a broken or leaking pipe is the source, have it repaired and remove the spilled waste. Sewer leaks under a building sometimes mean digging out the soaked soil.[1][2][4]
Where sources disagree
Development time: Colorado State gives about three weeks per generation at room temperature; NC State says about 10 days from egg through pupa, longer in cool conditions; Kentucky says about 10 days at around 93°F; and Texas A&M gives 14 to 37 days depending on conditions.[1][4][3][2]
Egg numbers: Colorado State says each female lays a few hundred eggs in total, Kentucky says females can lay 100 at a time, and NC State says a female can produce over 700 in her lifetime.[1][3][4]
Common questions
- Why do I keep getting tiny flies even after cleaning my drains?
- If they are phorid flies, the source may be hidden: a cracked drain pipe or sewer leak under the floor, a leaking appliance, or garbage. Sticky traps help show where flies concentrate.[3][1][2][4]
- Are phorid flies the same as drain flies?
- No. Both can come from drains, but drain flies are fuzzy and moth-like, while phorid flies are smooth, humpbacked and run before they fly.[2][1][4]
- Do phorid flies bite?
- No. Phorid flies don't bite; the problem is where they breed.[3][4]
Sources
- Colorado State University, Department of Agricultural Biology, “Phorid Fly/Drain Fly, Megaselia scalaris (Colorado Insect of Interest).” webdoc.agsci.colostate.edu/bspm/arthropodsofcolorado/Phorid-Flies.pdf (accessed 2026-11-11)
- Texas A&M AgriLife Extension, “ENTO-050: Indoor Flies and Their Control.” agrilifeextension.tamu.edu/library/insects/indoor-flies-and-their-control/ (accessed 2026-11-11)
- University of Kentucky Entomology, “ENTFACT-657: Small Flies.” entomology.mgcafe.uky.edu/ef657 (accessed 2026-11-11)
- NC State Extension, “Phorid Flies.” content.ces.ncsu.edu/phorid-flies (accessed 2026-11-11)
- Annual Review of Entomology, via PubMed, “Disney (2008), Natural history of the scuttle fly, Megaselia scalaris.” pubmed.ncbi.nlm.nih.gov/17622197/ (accessed 2026-11-11)
- American Journal of Tropical Medicine and Hygiene, via PubMed, “Hira et al. (2004), Myiasis in Kuwait: nosocomial infections caused by Lucilia sericata and Megaselia scalaris.” pubmed.ncbi.nlm.nih.gov/15100451/ (accessed 2026-11-11)
- Journal of Medical Entomology, via PubMed, “Singh and Rana (1989), Urogenital myiasis caused by Megaselia scalaris: a case report.” pubmed.ncbi.nlm.nih.gov/2724321/ (accessed 2026-11-11)
- Journal of Medical Entomology, via PubMed, “Solgi et al. (2017), Megaselia scalaris larvae as the cause of urinary myiasis.” pubmed.ncbi.nlm.nih.gov/28399213/ (accessed 2026-11-11)
- iNaturalist, “Megaselia scalaris taxon page (order and family).” www.inaturalist.org/taxa/329926 (accessed 2026-10-06)