Where Do Gnats Come From? What Attracts Them to a Bar
Quick Answer: "Gnat" is a size word, not one insect. In a bar, gnat-sized flies are usually fruit flies from spilled liquor, syrup, soda and ripe fruit, drain flies from the film inside drains, phorid flies from damp waste, and fungus gnats only if there are plants. Extension services in Texas, Oregon and Maryland point to the breeding site, not the adult fly.
People search "where do gnats come from" when small flies appear and they cannot see a cause. In a bar or kitchen the answer is almost always something wet and organic that nobody has cleaned. The sources below are university extension pages (checked October 2026), written for school kitchens and homes, not bars. To name the fly first, see types of flies in a bar.
What are gnats?
Gnats are small flies, and the word covers several species. Texas A&M AgriLife Extension (IPM Action Plan for Small Flies) calls the adult fruit fly "gnat-sized", up to one-eighth of an inch. It names four small flies common in food areas: drain flies, fruit flies, fungus gnats and phorid flies. Which one you have decides where to look, so match the fly to the place before you clean anything.
Where do gnats come from?
From the place their larvae develop, which is usually inside the building.
| Gnat-sized fly | Where it comes from | Source |
|---|---|---|
| Fruit fly | Fermenting fruit, vegetables and liquids; also wine, beer, juice and vinegar | Texas A&M; University of Maryland Extension |
| Drain fly | The gelatinous film in drains, grease traps and similar wet spots | Texas A&M; Oregon State |
| Phorid fly | Drains, garbage, damp organic matter, cracks in floors, under kitchen equipment | Texas A&M |
| Fungus gnat | Moist soil of over-watered potted plants | Texas A&M; Oregon State |
Texas A&M adds that large numbers of fruit flies may indicate spilled or spoiled fruit, poorly maintained garbage containers, buildup around drains, grout or broken tiles, and wet areas under and behind equipment.
What attracts gnats to a bar?
Sugar, fermentation and moisture. The University of Maryland Extension page on fruit flies says adults are attracted to overripe fruit, vegetables and fermenting foods, and that wine, beer, fruit juice and vinegar also attract them. It says damp mops and towels may hold enough food and moisture for development. Oregon State Extension (PNW 770) says biofilms form quickly in floor and sink drains, overflow drains and garbage disposals, and under antiskid floor mats. A bar can have several of these at once: sugary spills, a fruit tray, damp towels and a floor drain. See where bar fruit flies come from for the bar-side detail.
What are gnat eggs and larvae?
The early stages of the same flies, and they live where the food is. Fruit fly eggs are laid on the surface of fermenting food or liquid, and the University of Maryland says larvae feed for 5 to 6 days, with the whole life cycle taking 8 to 10 days. Oregon State says drain fly eggs are laid in groups of 10 to 40, and the larvae stay hidden in the slime on drain walls, so you rarely see them. Fungus gnat larvae feed on fungi and plant rootlets in soil. Our guide to fruit fly eggs and larvae covers what to look for. The two sources give different life-cycle times because they describe different flies.
Will a screen pourer stop gnats?
It stops one entry, not the source. Esatto makes and sells the Esatto Liquor Pourer with Screen, 12 Pack. It is our own product, not an independent pick. Its collection page describes a free-flow pourer with a built-in screen that keeps bugs and debris out of your liquor. That helps at the mouth of an open bottle. It does nothing for a drain, a bin or a damp mop. The screen pourers collection lists the other pack sizes. A sister site covers the dust-cap side in keeping pour spouts gnat free.
Frequently asked questions
Where do gnats come from in a kitchen?
From wet organic matter: spilled drinks, rotting produce, drain film, damp garbage and wet areas under equipment. The source depends on the fly.
What are gnats?
Small flies. The word is an everyday name, not a species. In food areas it usually means fruit flies, drain flies, phorid flies or fungus gnats.
What attracts gnats?
Overripe fruit, fermenting food, wine, beer, juice, vinegar and, for drain flies, the film inside drains. Fungus gnats are attracted to moist soil.
What do gnat eggs look like?
Drain fly eggs are tiny and unlikely to be visible, according to Oregon State. For fruit flies, see our guide to fruit fly eggs and larvae.
What do gnat larvae eat?
Drain fly larvae feed on bacteria, algae and fungi in drain film. Fruit fly larvae feed in fermenting food and liquid. Fungus gnat larvae feed on fungi and plant rootlets.
Do gnats come from drains?
Some do. Drain flies breed in the film inside drains, and a clear tape or cup over the opening overnight will show if flies are coming out of one.