Flies

Small flies in the house

Small house flies, generally under 1/8 inch, can breed entirely indoors. Insecticides alone rarely solve the problem: each kind breeds in a slightly different moist spot, so identify the fly, then find and eliminate where it breeds.[1]

The short answer

  • Fruit flies: remove overripe fruit and rotting vegetables and take out the trash; traps and sprays give only temporary relief.[1]
  • Drain flies: tape clear packing tape across part of a drain overnight; flies stuck to it mean the drain is a source. Scrub the pipe and trap with a stiff brush, since bleach and drain cleaner don't remove the film the larvae live in.[1]
  • Phorid flies: look for moist, decaying material, from garbage and drains to wet potting soil, and for leaks in sewer lines under the building.[1]
  • Moisture is the common thread: fly larvae can't develop without it.[1]

Fly profiles

Adult fruit fly (Drosophila melanogaster) with red eyes, with a 1 mm scale bar Fruit Fly Drosophila melanogaster Fruit flies, also called vinegar flies, are tiny flies drawn to ripe and fermenting fruits and vegetables; they are a problem year round but especially in late summer and fall. Sourced profile → Adult drain fly (moth fly), fuzzy with wings held roof-like Drain Fly (Moth Fly) Psychodidae (shown: Clogmia albipunctata) Drain flies, also called moth flies or filter flies, are small, fuzzy, non-biting flies whose larvae live in the slimy film inside drains, toilets and other places where water stands. Sourced profile → Adult fungus gnat, a slender dark fly with long legs and antennae Fungus Gnat Bradysia and related species Fungus gnats are small flies whose larvae live in moist potting mix and organic matter; indoors the adults emerge from houseplants and become a nuisance. Sourced profile → Adult house fly on a white surface House Fly Musca domestica The house fly is a worldwide companion of people and domestic animals; it breeds in garbage, manure and other moist organic matter and is most numerous in hot summer months. Sourced profile →

Phorid (humpbacked) flies

Phorid flies are about the size of fruit flies, 1/8 inch, tan to dark brown or black, with a humped back when seen from the side. They often run erratically rather than fly.[1][2]

  • Larvae develop in almost any moist, decaying material: garbage, drains, vase water, wet potting soil, broken garbage disposals, dead animals and feces. Egg to adult takes 14 to 37 days.[1]
  • Large numbers can mean a sewer leak under the building; contaminated soil sometimes has to be dug out.[1]
  • They're mainly a nuisance and not generally considered a health problem, though they can mechanically carry bacteria.[2]

Finding the breeding site

  • Clean up spilled or spoiled food on floors and in pantries, and clean sink and tub drains.[1]
  • Check under garbage can liners, under floor drain covers and floor mats, and under refrigerators and other appliances where debris collects; clean refrigerator and icemaker condensate pans.[1]
  • Hang mops to dry, and look for cracked or loose floor or bath tiles hiding wet films.[1]
  • Signs of rodents or wildlife can point to a dead animal, which breeds blow flies and phorid flies; seal entry points.[1]

Eye gnats outdoors

Eye gnats are tiny, 1/16 to 1/8 inch, dark flies that hover around eyes and any moist spots on people and animals. They don't bite but are a true nuisance and can spread diseases such as pinkeye. Larvae develop in freshly disturbed, well-drained sandy soils.[3]

Common questions

How do I know if flies are coming from my drain?
Lay clear packing tape across part of the drain opening, leaving some airflow, and check it over a day or two; flies stuck to the tape confirm the drain is a breeding site.[1]
Why doesn't pouring bleach down the drain stop drain flies?
Bleach and drain cleaners don't remove the bacterial film inside the pipes where the larvae live; scrub pipes and traps with a stiff brush.[1]
What are the tiny humpbacked flies running on my counter?
Likely phorid flies, which breed in moist decaying matter such as trash, drains and plumbing or sewer leaks.[2][1]

Photo credits

Sources

  1. Texas A&M AgriLife Extension, “ENTO-050: Indoor Flies and Their Control.” agrilifeextension.tamu.edu/library/insects/indoor-flies-and-their-control/ (accessed 2026-10-06)
  2. University of Minnesota Extension, “Humpbacked Flies (Phorid Flies).” apps.extension.umn.edu/garden/diagnose/insect/indoor/flies/small/humpbacked-flies.html (accessed 2026-10-06)
  3. Texas A&M AgriLife Extension, “Eye Gnat (Field Guide to Common Texas Insects).” texasinsects.tamu.edu/eye-gnat/ (accessed 2026-10-06)

Updated 2026-10-06. Built from sourced records. Spot an error? Tell us.