Fungus gnats are tiny, dark brown or black flies about 1/8 inch long with long legs, long antennae, and clear wings. They look similar to miniature mosquitoes and are one of the most common pests found around houseplants. If you’ve noticed small, slow-flying insects hovering near your potted plants or drifting toward windows, there’s a good chance you’re looking at fungus gnats.
Adult Fungus Gnats Up Close
An adult fungus gnat has a slender, elongated body that’s black or dark brown. At roughly 1/8 inch (about 3 mm), they’re small enough to be mistaken for specks of dirt until they move. Their two wings are delicate and clear, with a distinctive Y-shaped vein pattern visible under magnification. Unlike houseflies, which have compact, rounded bodies, fungus gnats have a narrow silhouette that looks more like a tiny mosquito.
Their legs are long and dangle below the body during flight, which is another mosquito-like trait. The antennae are longer than the head and made up of many small segments, giving them a beaded appearance. Their eyes are black and relatively small compared to other common household flies.
How They Move
Fungus gnats are weak, clumsy fliers. They tend to fly in short, darting bursts close to the soil surface rather than zooming around a room the way houseflies do. You’ll often spot them running across the top of potting soil, resting on leaves, or sitting on nearby walls and windowsills. Because they’re attracted to light, they frequently end up clustered near windows, which is where most people first notice them.
They don’t move far from their food source. If you see a handful of tiny dark flies hovering lazily around one particular plant, that behavior alone is a strong clue you’re dealing with fungus gnats rather than something else.
What the Larvae Look Like
The larval stage is the one doing damage to your plants, and it lives in the soil where you may not see it right away. Fungus gnat larvae are small, worm-like, and mostly translucent or white with a shiny black head capsule. That dark head is the easiest identifying feature. They’re typically found in the top inch or two of moist potting mix, feeding on fungi, decaying organic matter, and sometimes plant roots.
If you gently disturb the surface of damp soil and see tiny, thread-thin worms with dark heads wriggling around, those are almost certainly fungus gnat larvae. In heavy infestations, you may also notice shiny trails on the soil surface, similar to the slime trails left by slugs but much finer.
Fungus Gnats vs. Fruit Flies
This is the most common mix-up. Both are tiny flies that show up indoors, but they look and behave quite differently once you know what to check.
- Body shape: Fungus gnats are long and slender, like a small mosquito. Fruit flies are short and round, more like a miniature housefly.
- Eye color: Fungus gnats have small black eyes. Fruit flies typically have large, bright red eyes.
- Color: Fungus gnats are dark brown to black. Fruit flies range from tan to brownish, often with a lighter-colored body.
- Location: Fungus gnats hang around potted plants and soil. Fruit flies congregate near ripe fruit, drains, and fermenting food.
If the tiny flies are clustering around your kitchen fruit bowl, they’re fruit flies. If they’re hovering over the soil of your monstera or pothos, you’re looking at fungus gnats.
Fungus Gnats vs. Drain Flies and Shore Flies
Drain flies are another common indoor pest, but they look nothing like fungus gnats once you compare them side by side. Drain flies have broad, fuzzy, moth-like wings and a stocky body covered in fine hairs. They rest with their wings held flat, like a tiny triangle. Fungus gnats, by contrast, have narrow clear wings and a sleek body with no fuzz.
Shore flies are a closer look-alike. They’re roughly the same size and also show up around moist soil, especially in greenhouses. The key difference: shore flies are more robust and compact, resembling fruit flies in build, and their dark wings have five distinct light-colored spots. Fungus gnats are more delicate, with clear wings and that telltale Y-shaped vein.
Where You’ll Spot Them
Fungus gnats thrive wherever there’s consistently moist organic matter. Indoors, that means potted houseplants with soil that stays damp, especially if the mix contains peat or bark. You’ll see adults resting on the soil surface, running across leaves, sitting on nearby walls, or drifting toward the nearest window. Outdoors, they’re common around compost piles, wet mulch, and shaded garden beds.
A quick way to confirm an infestation is to place a yellow sticky trap near the base of a suspect plant. Fungus gnats are strongly attracted to yellow, and within a day or two you’ll have a clear sample to inspect. The trapped insects should match the description: tiny, dark, slender bodies with long legs and clear wings.