Gnats is a catch-all name for tiny, weak-flying flies. Indoors it almost always means fungus gnats (black, from houseplant soil), fruit flies (tan with red eyes, near food), or drain flies (fuzzy, gray, near sinks). Outdoors it can mean biting black flies or midges.

Why are there gnats in my house?

Something wet and organic is feeding the larvae: overwatered potting soil, produce going soft, a trash can with residue, recycling with beer or soda, slime inside a drain, or a hidden leak. Find that source and the gnats stop.

Fungus gnat larvae eat fungi, algae, and decaying plant matter in wet soil, and sometimes fine roots. Fruit flies eat yeast on fermenting food. Drain fly larvae eat the bacterial slime inside pipes. Adults mostly sip liquids.

What gets rid of gnats?

Removing the breeding source, plus the right trap for the gnat: yellow sticky cards and drier soil (or a Bti drench) for fungus gnats, a cider vinegar and dish soap jar for fruit flies, and scrubbing the drain for drain flies. Sprays alone do not last.

How do I keep gnats away?

Let houseplant soil dry between waterings, refrigerate ripe produce, rinse recyclables, take out trash often, clean drains monthly with a brush, empty drip pans and saucers, and keep window screens intact. A single trap left out shows you early if they return.

Indoor gnats are a nuisance, not a health threat. They do not bite. Fungus gnat larvae can damage seedlings and cuttings, fruit flies can carry bacteria onto food, and drain flies breeding in sewage are a sign of a plumbing problem.

Gnats in the House: What They Are and Where They Come From

Q: What do gnats look like?

Fungus gnats look like tiny black mosquitoes, about 1/8 inch, with long legs and antennae. Fruit flies are stockier and tan with red eyes. Drain flies are fuzzy, gray, and moth-shaped with wings held like a roof.

Q: How long do gnats live?

An adult fungus gnat lives 7 to 10 days and a fruit fly two to four weeks. The problem is reproduction: a fungus gnat female lays up to 200 eggs and a fruit fly about 500, and generations overlap, so the swarm persists until you remove the breeding site.

Gnats are tiny, weak-flying flies, and the ones in your house are almost always one of three insects: fungus gnats from houseplant soil, fruit flies from ripe food and trash, or drain flies from slimy pipes. None of them bite; they show up because something wet and organic in your home is feeding their larvae, and they leave when that source is gone.

That is the whole story in two sentences. The rest of this page helps you figure out which gnat you have, because the fix for one does nothing for the others. Sprays and foggers fail for all three for the same reason: they kill the adults you see, while hundreds of larvae keep developing out of reach.

What do gnats look like? The three house gnats

All three are 1/16 to 1/8 inch long, so look at color, shape, and where they hang out.

	Fungus gnat	Fruit fly	Drain fly
Color	black or dark gray	tan to brown, red eyes	gray, fuzzy
Shape	slender, long legs and antennae, like a tiny mosquito	stocky, rounded	wings held like a roof, like a tiny moth
Where	on soil, leaves, and windows near plants	kitchen, fruit bowl, trash	bathroom walls, sinks, tub
Flight	runs on soil, short weak flights	hovers, zigzags	short, weak hops
Breeds in	wet potting soil (top 2–3 inches)	fermenting food, trash, drains	slime inside drains, drip pans
Vinegar trap	ignores it	goes right in	mostly ignores it
Egg to adult	3–4 weeks at 65–75 °F	8–10 days	1–4 weeks

A quick test: water a houseplant. If a little cloud of black specks lifts off the soil, you have fungus gnats. If they circle a bowl of bananas, they are fruit flies. If they sit motionless on the shower wall and look like fuzzy triangles, they are drain flies. Pest pros on r/pestcontrol use another shortcut: if they will not go into a vinegar trap, they are not fruit flies. The gnats vs fruit flies page has close-up comparisons.

The fourth suspect: phorid flies. Small, humpbacked flies that run in jerky bursts across counters and walls are phorid flies. They breed in rotting organic matter, including sewage from a broken drain line, and they are the "gnats" behind most months-long, can't-find-the-source infestations in apartments.

Types of gnats outdoors

Outdoors "gnat" also covers insects that do bite. Black flies (buffalo gnats) breed in flowing streams and bite around the head and neck from spring into early summer. Biting midges (no-see-ums) live near marshes and coasts and bite at dawn and dusk. Eye gnats hover around your face in the South and West but do not bite. If something small is biting you, see gnat bites; none of these breed inside a house.

Why there are so many gnats in your house

Gnats seem to appear overnight because generations overlap. Colorado State University notes a fungus gnat female lays up to 200 eggs in moist, peat-rich potting mix; a fruit fly lays about 500. By the time you notice ten adults, there are usually hundreds of eggs and larvae in the source.

Common sources, roughly in order of how often they turn out to be the culprit:

Overwatered houseplants, especially in peat-based bagged potting mix, seedlings, old broken-down soil that holds water, and pots without drainage holes. Colorado State says fungus gnat problems peak in late fall and winter, when plants come indoors and need less water but get the same amount.
Produce going soft: bananas, tomatoes, a forgotten potato or onion at the bottom of the pantry bin.
Trash and recycling: a film of juice in the can, beer and soda cans, wine bottles, the lid of the kitchen bin.
Drains: kitchen sink, garbage disposal, sink overflow holes, a rarely used shower or basement floor drain.
Hidden moisture: the drip pan under the fridge or AC, a leaking toilet seal, a slow leak under a sink, a wet crawl space.

Fungus gnat larvae in wet potting soil: translucent worms with shiny black heads — Fungus gnat larvae live in the top inch of wet soil. If you see these, the plant is being overwatered.

Gnats can also come in from outside. Fungus gnats arrive in new potting soil or a new plant, and fruit fly eggs ride home on store produce. In summer and fall, they slip through window screens with gaps.

What do gnats eat?

Fungus gnat larvae feed on fungi, algae, and decaying organic matter in the top 2 to 3 inches of soil, and in large numbers on fine roots. Adults only drink water from leaf and soil surfaces.
Fruit flies feed on the yeast growing on fermenting sugar.
Drain fly larvae feed on the bacteria, algae, and fungi in drain slime.

How long do gnats live?

Adult fungus gnats live about 7 to 10 days, and fruit flies about two to four weeks; drain flies up to about two weeks. That sounds short, but generations overlap, so the population keeps going as long as there is a breeding site. Once you remove the source, expect adults to linger for 3 to 7 days (fruit flies) or 2 to 3 weeks (fungus gnats, whose larvae take longer to finish). If they are still there after a month, you have not found the real source.

Are gnats harmful?

To people, no. House gnats do not bite or sting. Fruit flies can carry bacteria from trash to fruit, so throw out anything they swarmed. Fungus gnat larvae can chew fine roots on seedlings and cuttings, though UC IPM points out that a wilting houseplant is more often suffering from overwatering and root rot than from the larvae themselves. Drain flies and phorid flies are a hygiene red flag: they only breed where organic slime or sewage builds up.

Disassembled sink P-trap with dark slime inside and a pipe brush — Drain slime is the nursery for drain flies and often fruit flies too.

Getting rid of gnats: the short version

The full plan with traps, products, and what fails is in how to get rid of gnats. In short:

Identify the gnat using the table above.
Remove the source. Let soil dry, throw out soft produce, clean the bin, scrub the drain, empty drip pans.
Trap the adults. Yellow sticky cards for fungus gnats, a vinegar-and-dish-soap jar for fruit flies, tape over the drain for drain flies.
Treat larvae if needed. A Bti product (Bacillus thuringiensis israelensis, sold as mosquito bits) watered into potting soil kills fungus gnat larvae and is toxic only to fly larvae.

What people who dealt with it say

Most "nothing works" stories are a wrong ID. In r/pestcontrol, r/homeowners, and r/Renters threads, people fought "fruit flies" with vinegar traps for weeks before learning they had fungus gnats from a plant, drain flies from an unused drain, or phorid flies from a leak.
Houseplant owners who win use two tools at once. In a long r/houseplants thread about "invincible" fungus gnats, the most upvoted fixes were beneficial nematodes or Bti in the water for the larvae, plus sticky traps for the adults. One person said mosquito bits never worked for them but a crushed mosquito dunk in the soil and the watering can did.
Sometimes it was never the plants. The top reply in that same thread: the "unmanageable" gnats vanished once a three-month-old bag of potatoes was found.
Hidden moisture is the pro's first question. When a homeowner with a crawl space reported hundreds of thousands of gnats, the replies were consistent: check the crawl space, sink, tub, and toilet seals, roof leaks, and the fridge condensation pan. A plumber can be more useful than an exterminator.
Bleach is a routine, not a fix. Renters report pouring bleach or drain products nightly for weeks; it can help if done consistently, but people who scrubbed the drain or found a dry trap or leak finished faster.

How to keep gnats away

Water houseplants only when the top inch or two of soil is dry, and empty saucers.
Use fresh, pasteurized potting mix when you repot; old mix holds more water.
Store ripe fruit in the refrigerator during warm months.
Rinse recycling before it goes in the bin and take out the trash every couple of days.
Brush out sink and shower drains monthly; run water in unused drains weekly.
Repair screens and close gaps around window AC units.
Leave one small vinegar trap and one sticky card out after an outbreak. If they start catching again, look for a new source right away.

When to call a pro

Gnats rarely need an exterminator. Consider one if gnats keep coming back after a month of source removal and you cannot find the breeding site, which can mean a broken drain line under a slab, a leak inside a wall, or a dead animal in a crawl space. A plumber with a camera is sometimes the better call than a pest company. Renters should report persistent gnats to the landlord in writing and ask for a plumbing inspection rather than another spray.

Gnats