The small gnats flying around your house almost certainly do not bite. The most common indoor gnats, including fungus gnats, fruit flies, and drain flies, lack the mouthparts needed to pierce human skin. They’re annoying, but physically harmless. That said, some gnat species that live primarily outdoors can bite, and occasionally find their way inside, which is likely why you’re wondering.
Common Indoor Gnats Don’t Bite
The tiny flies you see hovering near houseplants, kitchen fruit, or bathroom drains belong to a handful of species that have no interest in your blood. Fungus gnats are the most frequent offenders indoors. They’re dark, mosquito-like flies with long legs and segmented antennae, and they breed in the moist soil of overwatered houseplants. Adult fungus gnats don’t damage plants or bite people. Their entire presence is a nuisance, nothing more.
Fruit flies, the tan-colored specks circling your bananas, are similarly harmless. Drain flies, which look like tiny moths and congregate near sinks, feed on the organic sludge inside pipes. None of these species have cutting or piercing mouthparts. They simply cannot bite you, even if they land on your skin.
Which Gnats Actually Bite
A few outdoor gnat species do bite, and their bites can be surprisingly painful for such small insects. The main culprits are biting midges (also called no-see-ums, sand flies, or punkies) and black flies. These are different families of insects from the harmless gnats in your kitchen.
Only the females bite. Their mouthparts are specialized for cutting through skin and drawing blood, which they need to produce eggs. Males of the same species lack the ability to pierce skin. Female biting midges have mandibles that slice a small wound, then a tube-like structure that channels blood and saliva back and forth. They also have sensory organs on their mouthparts that help them locate warm-blooded hosts.
Black flies use a similar but rougher approach. The female cuts a hole in the skin and feeds on the blood that pools into it. During this process, she injects anticoagulants to keep the blood flowing, a pain-numbing compound to avoid detection, and proteins that trigger an allergic response afterward. The pain and swelling you feel are your immune system reacting to those foreign substances.
What a Gnat Bite Looks and Feels Like
If you are getting bitten, you’ll notice a sharp initial sting or pinch, followed by a red or discolored raised welt. The bites often appear in clusters or lines, especially on exposed skin like arms, ankles, and the back of the neck. Within hours, the area becomes intensely itchy, sometimes with mild swelling and a burning or tingling sensation. A black fly bite typically has a visible wound at the center of the welt.
The itching can last several days. Some people develop stronger allergic reactions with larger areas of swelling. Over-the-counter antihistamines and hydrocortisone cream help ease the itch. Avoid scratching, which can break the skin and invite secondary infection. In North America, biting gnats and black flies generally do not transmit diseases to humans, though biting midges have that potential in other parts of the world.
How to Tell What’s in Your House
Size and behavior are your best clues. Fungus gnats, fruit flies, and drain flies are typically less than a quarter inch long and cluster around specific food sources: potted plants, ripe fruit, or drains. They fly in lazy, erratic patterns and don’t follow you around. Biting midges are extremely small, often just 1 to 3 millimeters, and you might not even see the one that bites you, which is how they earned the name “no-see-ums.” Black flies are slightly larger, closer to mosquito size, and tend to swarm outdoors near rivers, lakes, or streams.
If you’re finding bites on your body but only seeing the typical kitchen or bathroom gnats, something else is likely biting you. Bed bugs, fleas, or even mosquitoes entering through gaps in screens are more probable explanations than the gnats near your houseplants.
Getting Rid of Indoor Gnats
Since the gnats in your house are almost certainly the non-biting kind, elimination comes down to removing their breeding sites. For fungus gnats, let the soil of your houseplants dry out between waterings. You can pull the plant from its pot to inspect for small, clear larvae in the soil. Avoid adding moisture-retaining materials like peat moss, and don’t bring new plants home without checking for signs of infestation. Sticky yellow traps placed near the soil surface catch adults effectively.
For drain flies, clean your sink drains at least once a week. Organic sludge builds up fast and gives them a steady food source. A simple home method: pour salt down the drain, followed by half a cup of baking soda and half a cup of white vinegar. The fizzing reaction helps break down buildup and kills flies and eggs in the pipe. For fruit flies, store ripe produce in the refrigerator and clean up any spills or fermenting residue on countertops.
Keeping Biting Gnats Out
If you live near water and biting midges or black flies are finding their way inside, standard window screens may not be enough. Most gnats are stopped by screens with 30 or more holes per inch, but no-see-ums at just 1 to 3 millimeters can slip through standard mesh. Screens with 50 or more holes per inch are needed to block them, though finer mesh does reduce airflow and visibility.
Proper installation matters as much as mesh size. Loose or sagging screens develop gaps that effectively widen the mesh spacing, letting small insects through. Make sure screens are mounted with consistent tension across the full surface, and seal the edges with weatherstripping or caulk where the screen meets the frame. Check doors and windows for any gaps, especially at the bottom corners where frames tend to separate over time.