How to Get Rid of Fungus Gnats in Your Houseplants (Because They’re Annoying and Gross)

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Got houseplants? Chances are you’ve got fungus gnats too. These teeny bugs are only about 1/16th of an inch long and often are seen flitting around near houseplants or in rooms where you have lots of greenery. Are they harming your plants? And how can you get rid of fungus gnats, anyway?

First, know that you’re not alone in your struggle to deal with these soil-dwelling pests. But fungus gnats are not as big of a problem as they might seem: “They’re not harmful to people or pets, but they are annoying,” says entomologist Michael Skvarla, PhD, assistant research professor of arthropod identification, Penn State University. “As their name indicates, they feed on fungus in houseplant pots, especially plants that stay moist.”

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Here’s what else you should know about your uninvited houseguests:

What Are Fungus Gnats?

Fungus gnats are the adult forms of the larvae, which are what feed on the naturally occurring fungus in houseplant pots. “The adults don’t feed at all. They have no functional mouth parts and survive from the energy reserve they built up as larvae,” says Skvarla. The adults have one job: to fly around and find a mate.

Once their task is accomplished, the females lay eggs in your houseplant’s soil. The masses of 100 to 150 eggs are so small that you won’t see them. They will become larvae—which also are impossible to see—and then adults. (Side note: Kinda gross, we know. But it’s just nature, so don’t freak out too much.)

At night, the adult fungus gnats hang out on walls or other surfaces and wait for daytime. However, they do fly toward light sources, such as a lamp in your living room or bedroom, in search of daylight, says Skvarla. That’s often when you’ll find them flitting around your face.

How Did my Plant Get Infected with Fungus Gnats?

Good question! Fungus gnats are everywhere outdoors; they’re so tiny and numerous that you won’t even see them sneak in when you open a door or window. Once inside, they look for a place to lay eggs, starting a new generation in your pots. The more houseplants you have, the more safe harbors they have. Sometimes, you also may bring home a plant that’s already infected, and it’s easy for them to spread to other houseplants.

Once they’re established, they continue to mate, lay eggs and hatch indoors, which is why you keep seeing them once you have them. Good news: The life cycle is pretty quick, and adults only live about 10 days. Bad news: “They can double their population in 17 days, so it doesn’t take long for the numbers to ramp up,” says Skvarla.

Do Fungus Gnats Hurt my Plants?

Not really. The only exception is if you are seed-starting something like tomatoes or peppers for your vegetable garden. If you have lots of seedlings and fungus gnats indoors in high density, the larvae could feed on the sensitive, young roots, which could kill the baby plants. But that’s a long shot and is more likely to happen in a greenhouse setting, not in just a few pots that will be growing in your home short-term before you plant them outdoors, says Skvarla.

How to Get Rid of Fungus Gnats: Close-up shot of fungus gnat stick on a trap below a cannabis plant
Martin Deja/Getty Images

How Do I Get Rid of Fungus Gnats?

You need to stop the cycle! First, if it’s a type of houseplant that can tolerate it, let the pots dry out completely in between waterings, which causes the eggs and larvae to become desiccated and die, says Skvarla. If the infestation is small and you occasionally let your pots dry out, you’ll get at least partial control.

Sticky traps, which you poke into the soil, are helpful for monitoring fungus gnat levels and can indicate what pots in which you may have fungus gnats. But you won’t be able to kill enough adults to wipe out every fungus gnat because the traps don’t contain an attractant— they just catch any fungus gnat which happens to flutter by, says Skvarla.

Sundews and other carnivorous plants set near other houseplants also can help catch the adults. In fact, these types of plants often are used for management of pests in greenhouse settings. However, while both sticky traps and carnivorous plants can be part of the solution, they usually won’t solve the problem entirely.

Unfortunately, there are no sprays or insecticides that are effective. You can use a biological control, a type of bacteria called Bacillus thuringiensis subspecies israelensis, or Bti for short. Bti is a larvicide that is specific to certain pests and it works well, though it may need reapplied periodically, says Skvarla. It’s often found in a granular form that is activated when watered into the soil surface.

If they don’t really bother you, you can just leave them alone. After all, they’re not going to hurt you, your pets, or your plants.

purewow author
Arricca Elin SanSone

Freelance Gardening Editor

Arricca Elin SanSone is a gardener with more than 15 years of experience. In addition to PureWow, she writes for Prevention, Country Living, Veranda, The Spruce and many other...
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