How to Get Rid of Gnats in Your House

What kind of gnats do you have?

"Gnat" is not one insect. People use the word for at least three tiny flies that turn up indoors, and each one breeds in a different place. Getting this right first saves you from drying out plants that were never the problem, or scrubbing drains while the gnats keep hatching in a flowerpot.

Fungus gnats are slender black flies about 1/8 inch long with long legs and long antennae ^[1]. They tend to run across the soil surface and flutter weakly around plants. UC IPM points out that their antennae are longer than their head, which separates them from shore flies with short, bristle-like antennae ^[2].

Fruit flies are about the same size but tan in front with a darker rear and red eyes, and they hover around ripe fruit and the trash ^[4]. Drain flies are fuzzy, dark gray flies whose hairy wings fold roof-like over the body, and they usually rest on walls near sinks and tubs ^[5].

Clue	Fruit fly	Fungus gnat	Drain fly
Color and shape	Tan front, dark rear, red eyes	Slender, black, long legs	Fuzzy, gray, moth-like wings
Where you see it	Fruit bowl, trash, wine glass	Houseplant soil, nearby windows	Bathroom walls, sinks, tubs
How it moves	Hovers slowly around food	Runs on soil, weak short flights	Short, hopping flights
What fixes it	Remove fermenting food	Let soil dry	Scrub the drain film
Full guide	Fruit fly guide	This page	Drain fly guide

If the gnats gather around houseplants, treat the soil; if they gather around food or drains, the plants are not your problem. Still unsure? Try the bug identifier or compare photos on the fungus gnat profile and fruit fly profile.

Why are there gnats in your house?

Fungus gnats point to potting soil that stays wet. Minnesota Extension links them to overwatered soil or soil rich in organic matter, found mostly around houseplants ^[3]. A female lives about 7 to 10 days and can lay up to 200 eggs into cracks in the soil. The larvae, which are translucent with a shiny black head, feed on fungi, algae and decaying plant matter in the top 2 to 3 inches, and they also chew fine roots ^[1].

Development is quick. At 75 F, eggs hatch in about 3 days, larvae grow for about 10 days and adults emerge about 4 days after that, roughly 17 days per generation ^[2]. Colorado State gives three to four weeks at 65 to 75 F.

Fall and winter are the worst time. Colorado State explains that plants brought indoors after a summer outside often carry gnats in, and that winter watering keeps the soil moist ^[1]. In rare cases, Minnesota Extension notes, fungus gnats can develop inside damp walls where fungus grows ^[3].

How do you get rid of fungus gnats step by step?

Colorado State calls drying the growing medium the single most important step ^[1]. Work through every pot in the house, not only the one where you saw gnats:

1. Find the infested pots. Push a few 1/4 inch slices or wedges of raw potato into the soil surface. After a few days, turn them over; larvae gather on the underside. Replace the slices with fresh ones as you keep checking ^[2].
2. Let the soil dry. Water only when the top 1 to 2 inches feel dry. Larvae need moisture, so this starves the next generation.
3. Fix drainage. Use pots with drain holes, and pour out water that collects in saucers and decorative cachepots. UC IPM advises avoiding overwatering and providing good drainage.
4. Clean up the soil surface. Pick off fallen leaves and remove rotting bulbs or roots. Repot plants whose mix stays soggy or smells sour.
5. Trap the adults. Stand yellow sticky cards at the edge of each pot or just under the leaves. They catch egg-laying females, and the count tells you whether the problem is shrinking ^[1].
6. Check other damp spots. If gnats persist with dry pots, look for wet organic material elsewhere, such as a leaking pipe, a soggy planter on a sunporch or compost scraps.

Sticky cards and drying the soil work together: the cards remove adults, and dry soil stops new ones from growing. Expect to keep at it for at least one full life cycle, about three weeks, before judging the result.

What about Bti, nematodes and insecticides?

For houseplants, insecticides are rarely warranted, according to UC IPM ^[2]. Try the drying steps for a few weeks first. If larvae are still turning up on potato slices, two biological options exist:

Option	What it is	What sources say	Limits
Bti soil drench	A bacterium (Bacillus thuringiensis subsp. israelensis) that kills gnat larvae	Applied to the soil to kill larvae	Does not persist indoors; UC IPM notes repeat applications at about 5-day intervals
Beneficial nematodes	Tiny worms (Steinernema feltiae) applied in water	Colorado State reports larval kill within three to four days	Living organisms; check the product directions for indoor pots
Insecticide for adults	Short-residual products such as pyrethrins	UC IPM: temporary, fast-acting control if nothing else works	Does not stop larvae; harmful to beneficial insects

Sources for the table: Colorado State University Extension ^[1] and UC IPM ^[2], retrieved 2026-11-12.

Bti and pyrethrin products are both pesticides, even when they are biological. Choose an EPA-registered product whose label lists fungus gnats and indoor plants. Read and follow the label. The label is the law. Keep children and pets away from treated plants as the label directs, and store products out of their reach ^[6]. UC IPM suggests treating houseplants outdoors when possible and waiting about a day before bringing them back inside. Do not pour homemade mixtures of household chemicals into pots.

How do you keep gnats from coming back?

Fungus gnats can show up in any month, but nuisance problems peak in late fall and winter ^[1], when plants come in for the season and dry indoor air tempts people to water more.

A few habits keep the soil unfriendly to larvae:

• Water by need, not by calendar. Push a finger into the soil and wait until the top inch or two is dry.
• Before bringing summer plants indoors, check them with potato slices and let the soil dry.
• Keep extra potting mix sealed and dry; open bags that stay damp can start a new population.
• Leave a yellow sticky card in a few pots through winter as an early warning.
• Group plants where you can see them, such as a bright corner of the living room, so a new outbreak gets noticed early.

When should you call a professional? Fungus gnats in houseplants almost never need one. If gnats keep emerging from a wall, floor or crawl space with no plants nearby, a hidden leak may be feeding fungus in the structure, and a licensed pest professional or a plumber can help find it. Browse our other pest removal guides for more help.