Fungus gnats around the houseplants, and why they get worse in winter

What are fungus gnats?

They're tiny, dark flies that look like mini mosquitoes, and they breed in damp potting soil.

Look-alikes

Fungus gnat or fruit fly?

1 2 3

Fungus gnatBradysia, a dark-winged fungus gnat

vs

1 2 3

Fruit flyDrosophila melanogaster

How to tell a fungus gnat from a fruit fly

Look at	Fungus gnat	Fruit fly
1Body	Slender, like a tiny mosquito	Stout, with a cylinder-shaped body
2Antennae	Like a string of beads	A feathery bristle at the tip
3What stands out	Long, thin legs, and wings that are clear or dark	Eyes that are usually reddish

Their larvae are about 1/4 inch long, white and legless, with shiny black heads. They eat roots, or the fungus growing in your soil.

Do they hurt your plants? Mostly they just bug you. But in big numbers the larvae can damage roots and stunt growth, especially in seedlings and young plants, UC IPM says. And if a plant's drooping, water trouble or root rot is more often to blame.

Picture this: a gray January afternoon, a video call with your boss, and one tiny dark fly that keeps darting across the screen like it has something to add. You swat at it twice, miss twice, and now the whole call has watched you lose to a gnat.

Is it a fungus gnat or a different tiny fly?

Where you see them is your best clue. Around the pots? Probably fungus gnats. By the fruit bowl or trash, think fruit flies. By a sink drain, think drain flies. Each kind likes a slightly different spot, so Texas A&M says to name the fly first.

Which one is it?

Which tiny fly is it?

Pick where you see them most for our best guess and what to do next.

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Probably fungus gnats Dry out the soil

They most often come up out of houseplant soil, Texas A&M says. Let the top 1 to 2 inches dry before you water again, and dump any water sitting in the saucer. The rest of the fix is on this page.

Probably a fruit fly Find the fruit

Fruit flies are stout and usually have reddish eyes. At home they breed mostly in overripe or damaged fruit, bananas especially, and in spoiling vegetables, Texas A&M says. Toss the soft fruit and take out the trash.

Probably a drain fly Check the drain

Drain flies look fuzzy and moth-like, and they usually fly only a few feet at a time. Lay clear packing tape across the drain without covering the whole opening, and check it now and then. Flies stuck to it mean that drain is a source, Texas A&M says.

Maybe fungus gnats from the drain Try the tape test

Some fungus gnats may also feed on the film inside drains, the same as drain flies, Texas A&M says. Lay clear packing tape across the drain without covering the whole opening. Flies stuck to it mean that drain is a source.

Maybe a hackberry psyllid Vacuum them up

Texas A&M's bug expert in Travis County said in 2017 that this tiny fall bug is often mistaken for a gnat. They get inside and collect on windowsills, and she said they're harmless and vacuuming is probably the best fix. Kentucky says they may come in through window screens, and they may probe your skin but don't feed on people. Fungus gnats are drawn to light too, though, so check any pots nearby.

Probably springtails Not a fly

Springtails have no wings and don't fly. They jump like tiny fleas, they sometimes turn up in potted plants, and they don't bite, Texas A&M says. See springtails

Hard to tell from here Worth a call

Call or text 843-480-8699 and tell us what you're seeing. We can usually identify it over the phone. See what the plan covers

One twist: some fungus gnats may also feed on the film inside drains, like drain flies do. So a gnat by your sink isn't always a drain fly.

If you see gray specks hopping on wet soil, those are probably springtails, which jump instead of fly. They don't even have wings, Texas A&M says.

Why are there gnats in the house in winter?

Because that's when your potting soil tends to stay wet. Texas A&M says these houseplant infestations are most common in the winter months, when overwatering is more common.

Colorado State says shorter days and cooler temps slow how fast a plant grows and uses water. If you keep watering like it's summer, the soil stays moist, and that helps the gnats.

In our count of U.S. Naval Observatory sun data, an Austin December day averages 3 hours 50 minutes less daylight than a June day.

An Austin December day averages 3 hours 50 minutes less daylight than a June day

Our count of U.S. Naval Observatory sunrise and sunset times: the average daylight each month, in hours and minutes. Winter months are orange.

• Winter months
• The rest of the year

The larvae usually live in the top few inches of wet soil, so if you're hunting houseplant bugs, start there. In some cases a new bag of potting soil brings them in, Texas A&M says. For the rest of the year, check our month-by-month Austin pest calendar.

How do you get rid of fungus gnats?

Dry out the top of your soil and take away their wet spot. Texas A&M says the only real fix is finding where they breed and getting rid of it.

• Check the pot. In a bigger pot, push a 1/4 inch slice of peeled potato into the soil. Any larvae will move to it within 24 to 48 hours, Colorado State says.
• Add a sticky card. A yellow card at the pot's edge catches adults. On its own, it won't cut their numbers much.
• Let the top dry. Water only when your plant needs it, and let the top 1 to 2 inches dry first. A dry surface kills eggs and larvae. Dump the saucer, too.
• Still flying? Once they're a problem, drying alone may not be enough, Texas A&M says. You can treat or replace the pot and soil, or move the pots outdoors.

No larvae in the potato, and the flies keep coming? Call or text us at 843-480-8699 and tell us what you're seeing. We can usually identify it over the phone.

Do Mosquito Bits work on fungus gnats?

They can, on the larvae in the soil. Mosquito Bits are Bti granules, and the EPA-accepted label has directions for gnat larvae in house plant soil.

Sprinkle 1 to 2 teaspoons on a small pot (6 inches across or less) or 1 tablespoon on a bigger one, and water it in. If gnats come back within 3 weeks, do it again. Or soak 4 tablespoons in a gallon of water for 30 minutes and skim off the granules. Water the soil with it weekly for three weeks. Follow the label on your own bag, and read its CAUTION line: harmful if inhaled or absorbed through the skin, and it causes moderate eye irritation.

Bti works on the larvae that eat it, so the adults already flying hang around until they die off. Young larvae are hit hardest, says NPIC, a pesticide info center. And in a 2006 lab study, a Bti drench did nothing to larvae in their second and third stages. So start early, and repeat it the way your label says.

Can pest control get rid of fungus gnats?

For gnats in a houseplant, the real fix is in the soil. Sure, gnats are on the list our plan covers. We treat outside by default, and inside when you ask, at no extra cost. But the larvae live in the pot, and sprays won't solve that, Texas A&M says.

A visit makes sense when the flies may not be from a pot: tiny flies in rooms with no plants, or no larvae in the potato. Our plans from $97 a month are billed monthly and cover 40+ pests on every visit. Here's how a visit every two months works.

Tried all that and they're still flying? Call 843-480-8699 or get a free quote right here.

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