Gnats and fruit flies: what the tiny flies are, and where they come from
Published Updated
By John Stopka, Co-Founder & CEO · Reviewed by John Stopka
The tiny flies in a kitchen or bathroom are usually one of four: fruit flies, tan with red eyes, around ripe fruit and recycling; fungus gnats, small and dark, around houseplants; drain flies, fuzzy and moth-like, on the walls near a sink or shower; or phorid flies, humpbacked and running in short bursts. None of them bite. Each breeds in one kind of place, and they keep coming back until that place is found and cleaned out.
Which tiny fly is it?
| Fly | Looks like | Found | Breeds in |
|---|---|---|---|
| Fruit fly | about 1/8 inch, tan, bright red eyes | kitchen counters, fruit bowls, trash and recycling | ripe or rotting fruit and vegetables, spills, the film in drains and bins |
| Fungus gnat | tiny, dark, long legs, weak flier | around houseplants and windows | damp potting soil |
| Drain fly | fuzzy, gray, moth-like wings held flat | resting on bathroom and kitchen walls | the slime layer inside drains |
| Phorid fly | small, humpbacked, tan to dark | running across counters and walls | wet, decaying matter; drains; in stubborn cases a broken drain line under the floor |
Fruit flies
The classic kitchen fly. Fruit flies are drawn to fermenting fruit and vegetables, and they lay their eggs on the surface of it; a single forgotten potato or onion at the back of a cupboard can keep a population going. In warm weather they go from egg to adult in about a week or two, which is why a few become a cloud so quickly.
The fix is finding every source: overripe fruit, produce stored at room temperature, spills under appliances, recycling bins with a little juice or wine left in the bottles, garbage disposals and the film inside drains. A small dish of cider vinegar with a drop of dish soap shows whether they are still around, but it will not end the problem while a source remains.
Fungus gnats
Small, dark, long-legged flies that drift weakly around houseplants and gather at windows. Their larvae live in damp potting soil and feed on fungi and organic matter in it. Overwatering is almost always the cause. Letting the top inch or two of soil dry out between waterings, and removing standing water from saucers, usually breaks the cycle.
Drain flies
Fuzzy little flies with rounded, moth-like wings, usually sitting still on a wall beside a sink, tub or shower. They breed in the gelatinous film that builds up inside drains and overflows. Pouring products down the drain rarely helps; scrubbing the film out of the drain and overflow is what removes them. Drain flies in a commercial kitchen are covered on our restaurant pest control page.
Phorid flies
Small, humpbacked flies that tend to run across surfaces in short, jerky bursts rather than fly off. They are often mistaken for fruit flies. Phorid flies breed in wet, decaying organic matter — drain buildup, garbage, and in stubborn cases a broken drain or sewer line under a slab floor — and, like drain flies, they keep coming back until the place they are developing is found and cleaned out.
Do gnats bite?
The gnats and tiny flies that breed in homes — fruit flies, fungus gnats, drain flies and phorid flies — do not bite people. The biting "gnats" people meet outdoors are different insects, such as black flies and biting midges, which breed in water and wet ground outside rather than in the house. If a bite concerns you, contact a healthcare provider.
Why do gnats keep coming back?
Because the flies you see are the adults, and the next generation is already growing somewhere out of sight: in a drain, a potting pot, a bin or a forgotten bag of produce. Spraying the adults in the air does little. Finding and cleaning out where they are developing is what ends it.
How does Liberty handle gnats and small flies?
Liberty treats gnats and small flies, alongside the everyday pests our pest control plans cover, starting by finding where they are breeding. Text us about what you are seeing and where, or book a free inspection. For larger flies, see our flies in the house article.
When to call a professional
Call when small flies keep coming back after you have cleared the fruit, dried out the plants and cleaned the drains — especially humpbacked flies that run rather than fly, which can point to a drain problem under the floor.
Common questions
What are the tiny flies in my kitchen?
Usually fruit flies — tan with red eyes, around fruit, trash and recycling. Small fuzzy flies on the walls near a sink are drain flies, and small dark flies around houseplants are fungus gnats.
Do gnats bite?
The gnats that breed in homes do not bite. Biting gnats such as black flies and biting midges are outdoor insects.
Why won't the fruit flies go away?
Because a source is still there — overripe produce, a spill, a drain or a recycling bin. The adults come back until every place they are breeding is found and cleaned out.
What causes fungus gnats?
Damp potting soil. Their larvae live in it, so letting the top of the soil dry out between waterings usually ends them.
Does Liberty treat gnats and fruit flies?
Yes. Liberty treats gnats and small flies, starting by finding where they are breeding.
Sources
- University of Kentucky Entomology. Michael F. Potter. "How to Pest-Proof Your Home" (ENTFACT-641). https://entomology.mgcafe.uky.edu/ef641 (opens in a new tab)