How To Get Rid of Fungus Gnats, a Common Houseplant Pest

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If you’ve been spending more time at home lately because of the coronavirus pandemic, you may have noticed some unwelcome houseguests hanging around—tiny black insects that hover around your houseplants. Those, dear friend, are fungus gnats.

But what exactly are fungus gnats, and how do you get rid of them? Whether you have a full-blown infestation or just a few houseplant pests, here’s everything you need to know.

Fungus gnats vs. fruit flies: What’s the difference?

Fungus gnats are typically between one-16th to one-eighth of an inch long—so they’re pretty darn tiny, and often misidentified as fruit flies. Make sure you know the difference first.

“Before you take any kind of control measures for any pest, it’s important to identify them first and find out where they are, and the conditions that are leading to their presence,” says Karey Windbiel-Rojas, associate director for urban and community integrated pest management at the University of California Division of Agriculture and Natural Resources.

Unlike fruit flies, which look like small, common houseflies, fungus gnats have skinny, delicate-looking bodies and legs, long antennae, and wings with a distinct Y-shape vein (if you can stomach the idea of getting a closer look).

Fungus gnats are often found flying or crawling around indoor potted plants, but they’re also attracted to light, which means you might notice them near windows or lamps. They don’t typically fly great distances and tend to stick close to houseplants.

You also might find fungus gnats outside in your yard, near piles of wet mulch or compost. Fungus gnats have also been known to hang out in wall or floor voids, particularly after new construction or when there’s some sort of moisture issue, like a leaky faucet.

Where do fungus gnats come from?

“Fungus gnats feed on decaying plant matter and fungi and thrive in moist conditions, such as soil, which is where they lay their eggs,” says Derek Gaughan, founder of the DIY pest control website Bug Lord. “If you own a lot of houseplants, you are more susceptible to having a problem as this is their ideal habitat.”

With so many of us working from home these days—and at risk of overwatering our plants—it’s no surprise that these critters are out in full force. How many times a day have you walked by your favorite houseplant and decided to water it?

“The best thing you can do is avoid overwatering your plants and to let the soil dry out between waterings,” says Gaughan.

You might also notice an infestation of fungus gnats shortly after repotting your houseplants or after bringing new plants into your home. This is because bugs sometimes hitch a ride inside bags of potting soil or plants from home improvement stores. They can also make their way indoors if you set your houseplants outside to get some sunlight then bring them back in.

How to make DIY traps for fungus gnats

While fungus gnats don’t bite and won’t necessarily damage your plants (though they can if you have a really bad infestation), they are annoying, so you’ll want to get rid of them.

You’ll want to start by getting sticky traps to catch adults and determine the scope of your problem. These traps are typically yellow (fungus gnats are attracted to the color) and attach to a wooden stick that you push into the soil of your plants.

You can even make sticky traps at home by smearing yellow strips of paper with petroleum jelly, according to gardening expert Gary Pilarchik (video tutorial below).

The traps will kill some adult fungus gnats, but more importantly, they’ll let you know whether you need to take further action. Have one or two gnats on your trap? It’s probably not a huge deal, and you can try watering your plants less first. Have dozens? Yikes! It’s time to consider stronger pest control tactics.

Natural, nonpesticide ways to get rid of fungus gnats

If you don’t want to spray pesticides in your house and prefer to try a natural method first, you can spray a solution of soapy water on the plant’s leaves, says Frank Meek, a board-certified entomologist and the international technical and training director for Orkin.

“Mix soap and water, and apply it to the foliage of the plant with a fine-mist spray bottle,” Meek says. Generally a concentration of one tablespoon dish soap in a quart of water is strong enough to deter fungus gnats without bothering your plant.

Soap and water method not working? Then you may want to break out the big guns and bring in nematodes. Nematodes are microscopic worms, available at garden supply and home improvement stores, that dig into the soil and feast on fungus gnat larvae—and they don’t cause any harm to your plant in the process. You simply spray or sprinkle them onto the soil, then let them do all the hard work.

If none of these solutions is working for you, it might be time to consider a pesticide. But before you grab the first chemical pesticide you see at the store, take time to do some research first. Most pesticides are designed with specific types of pests and plants in mind, so thoroughly read the labels. And always follow the directions before using the pesticide to ensure the safety of your family members, pets, and the environment overall.

“Homeowners can use interior plant pesticides as long as the type of plant is listed on the product label,” Meek says.

If these methods fail, or you’re dealing with fungus gnats inside your walls or floors, you might need to call in a pest control professional.

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