What Causes House Gnats, and What Is the Fastest Way to Get Rid of Them?

Medically Reviewed on 12/8/2021

The types and nature of house gnats

House gnats are those tiny grayish-black flies usually found around house plants. They are attracted to plants and decaying organic matter and the fastest way to get rid of them is by using traps and diluted bleach.
House gnats are those tiny grayish-black flies usually found around house plants. They are attracted to plants and decaying organic matter and the fastest way to get rid of them is by using traps and diluted bleach.

House gnats are those tiny grayish-black flies usually found around house plants. Although house gnats are harmless, they can be really annoying, since they fly all over the place. Because house gnats constitute such a nuisance, you should know how to prevent their infestation or eradicate them quickly.

There are three major types of house gnats.

  • Fungus gnats
  • Fruit flies (vinegar or pomace flies)
  • Drain flies (phorid flies)

Fungus gnats are usually black and small. They are attracted to plants and decaying organic matter. They typically lay their eggs in the soil of in-house potted plants. The presence of moisture and rotten leaves in the soil of indoor potted plants encourages the breeding of fungus gnats. 

Fruit flies are usually small and brown with red eyes. They love overripe or rotten fruits and vegetables as well as vinegar and alcohol. The presence of overripe or rotten fruits and food in the house or kitchen encourages the breeding of fruit flies.

Drain flies (or, phorid flies) closely resemble fruit flies, but they have black eyes (not red, like the fruit flies) and walk in a zigzag pattern. Phorid flies breed well in moist areas of the house, e.g., drains in the kitchen or anywhere there is a leak or sewage in pipes or sinks.

Knowing the peculiarities of each type of gnat helps identify which kind of house gnats you're dealing with. This makes it easier to eliminate them.

Causes of house gnats

So, what causes gnats in the house?

  • Abandoned fruits. Fruit flies love fruits. They multiply and swarm the house whenever fruits are left unattended and begin to rot. Therefore, fruits and drinks made from fruits or other sugary substances will, sooner or later, attract fruit flies when left exposed in bowls, shelves, or on countertops.
  • Overwatered plants. Too much moisture in the pots of in-house plants produces a good breeding ground for the eggs and larvae of fungus gnats, so, if you overwater your plants, you may be attracting house gnats.
  • Delayed emptying of kitchen trash cans. There's usually lots of moisture and decomposing organic matter (leftovers of food, bones, vegetables, etc.) in kitchen trash cans. Therefore, a delay in emptying these trash cans can invite house gnats.
  • Too much moisture in bathrooms and kitchens. Drain gnats multiply when moisture builds up in bathrooms and kitchens, so you may attract drain gnats if you have faulty pipes, vents, and sinks in your home.
  • Fruit-scented hygiene and beauty products. Gnats are attracted to anything that smells fruity and sweet. Therefore, fruit-scented hygiene and beauty products tend to draw gnats into the house.
  • Rotting food in the drain. A buildup of food in the drain would, over time, result in an infestation of house gnats. Why? Because house gnats are drawn to decomposing organic matter. 

How do you get rid of gnats in your house?

Getting rid of house gnats is quite simple, and you might not always need chemicals or pesticides to eliminate gnats in your house. So, what's the fastest way of getting rid of house gnats? 

Construct apple cider vinegar traps. Combine a few tablespoons of apple cider vinegar, a few drops of dish soap, and one tablespoon of sugar in a bowl. Now, stir the content and place the bowl in locations frequented by gnats (such as your kitchen or bathroom). The sugar and apple cider vinegar mixture attracts gnats, while the dish soap traps and drowns them. 

Make fruit traps. You can make fruit traps to get rid of gnats. Do this by covering jars of rotting fruits with perforated plastic wrap. Alternatively, you can insert a paper funnel into the baited jar. This will attract gnats and get them trapped inside.

Pour diluted bleach down the tub or sink drain. If gnats are near the sink in your kitchen or bathtub, you can dilute some bleach and pour a cup of the solution down the drains to eliminate the infestation. 

Seek the services of a professional pest control company. If you're dealing with a persistent gnat infestation, you can hire a professional pest control company to assist you. The best pest control companies are knowledgeable about treating both adult gnat and gnat larvae. In addition, they can help you with a customized treatment plan. 

Furthermore, the following should be done to prevent house gnats.  

  • Keep fruits and vegetables well refrigerated.
  • Keep the kitchen and shower drains clean.
  • Empty the trash promptly. Have a schedule and stick to it.

To deal with drain gnats, it's essential to disrupt the breeding sites in the drain using a stiff brush. After a thorough scrubbing, it's advisable to flush the drain with hot water to remove any material left in it. Alternatively, a drain antibacterial product could be used, e.g., S-hydroprene (Gentrol). This product is an insecticide that has low toxicity and prevents the larvae from completing metamorphosis.

House gnats are not known to spread any disease, but they indicate the presence of unhealthy substances in your living environment. If you don't attend to these unhealthy substances, they may affect your health. 

Check with your doctor

Consult your doctor if you have unusual itching, diarrhea, or stomach problems after you use insecticides to control house gnats.


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Medically Reviewed on 12/8/2021

IOWA State University Extension and Outreach: "Watch for Fungus in the House and Take Action if Found."

Texas A&M AgriLife Extension: "Indoor Flies and Their Control."

University of Kentucky College of Agriculture, Food and Environment: "Fruit Flies."