Proving that small insects can be big pests, gnats often become nuisances in damp locations inside homes. The word "gnat" is the common term for various small, flying insects that belong to the insect order Diptera. Common household gnats include fruit flies, drain flies and fungus gnats, all harmless pests that feed on decaying organic matter, as well as biting gnats known as "no-see-ums." Fortunately, you can get rid of gnats using various control methods.
Types of Household Gnats
Fruit flies (Drosophila spp.), also called vinegar or pomace flies, are 1/8 inch long flying pests that earned their name because they commonly hover around overripe fruit. Despite this, the tiny black flies congregate anywhere with consistently moist, fermenting organic materials. In fact, they most commonly congregate in the slime that builds up inside of sluggish or rarely used drains. Other moist locations that attract fruit flies include dirty household trashcans, containers of stale soda or beer, wet towels or rags, areas around dripping or leaking pipes and refrigerator drip pans.
Drain flies (Psychoda spp.), sometimes called moth, filter or sewage flies, are small, fuzzy mothlike pests that range from 1/6 to 1/5 inch in length. As the name implies, these pests like dirty drains, with the females laying egg masses in the gelatinous gunk that builds up when organic matter decays. They'll also develop around leaking or broken drainpipes and refrigerator drain pans.
No-see-ums (Culicoides spp.) are tiny gnats that deliver painful bites. Sometimes called punkies and biting midges, these pests typically live outdoors where the females lay eggs in wet soil around ponds, creeks and air conditioners. Adults typically reach no larger than 1/16 inch long and look like tiny, compact mosquitoes. Their diminutive size allows the pests to easily slip through standard window screens, and the females bite people and pets because they must feed on blood for their eggs to be viable.
Fungus gnats (Bradysia spp.), the most common type of gnats in homes, look like small mosquitoes and have dark-colored bodies that reach about 1/8 inch long. These pests also thrive in moist locations but prefer the soils of overwatered houseplants. Allowing the top 2 inches of soil to dry between waterings is a simple way to keep fungus gnats at bay. The pests don't fly very well, so you'll typically see them hovering around their host plants or hopping across the surface of the soil.
The first step to getting rid of household gnats is to eliminate moisture and decaying materials. Follow these sanitation practices:
- Use plastic liners inside bedroom, kitchen and bathroom trashcans.
- Empty trash daily and clean trashcans when waste builds up.
- Avoid leaving trash out overnight or dirty dishes in the sink.
- Discard overripe fruit and rotting vegetables.
- Place still-ripening fruits and vegetables in the fridge.
- Clean up any spilled liquids and food debris promptly.
- Rinse all containers before placing them in recycling bins. Don't store recycling for more than a week
- Promptly repair plumbing leaks.
- Get rid of stagnant water inside your home, including water in mop buckets, saucers beneath potted plants and the drip pan beneath your fridge.
- Avoid leaving wet towels or rags lying out overnight.
- Clean out garbage disposals.
- Clean the slime out of infrequently used drains.
Because household gnats like the gelatinous film that builds up in rarely used or sluggish drains, cleaning up the slime helps make your home unattractive to these pests. Simply pour hot tap water down the drain to loosen up slime and scrub the pipes with a long-handled, stiff wire brush or a plumber's snake. Flush the cleaned pipe by slowly pouring more hot water down the drain again.
Gnats frequently make their way indoors to get away from very cold or very hot temperatures. To exclude them:
- Install tight-fitting screens finer than 14 mesh over windows and doors as well as vents to the outside. Larger mesh allows household gnats to fly right through the little holes.
- Inspect screens regularly for tears, and fix tears promptly.
- Fill cracks on the outside of your home with foam or caulk.
- Place weatherstripping around door edges and kick plates below exterior doors.
- Spray screens with a permethrin-based aerosol insecticide to stop gnats from coming inside.
Physically removing pesky gnats is an easy way to get rid of the pests. You can:
- Whack them with a fly swatter.
- Suck up gnats with a vacuum cleaner.
- Hang flypaper or resin strips in infested areas. Change flypaper every three months or when the strips become covered with dead gnats.
- Pour a little vinegar into a shallow container
and place it where you often spot fruit flies congregating. The vinegar
attracts the pests and they drown in the liquid.
Only use pesticides to supplement sanitation and exclusion methods. Remember that pesticides might get rid of adult pests but don't offer long-term control. Pyrethrin-based pesticides specifically labeled for use against "flying insects" or "gnats" effectively control gnat populations temporarily. A hydroprene-based pesticide in foam or spray form works effectively to treat fruit fly breeding locations. Hydroprene is an insect growth regulator that affects only gnat larvae.
For fungus gnat-infested houseplants, drenching the soil with a product containing the bacterium Bacillus thuringiensis 'israelensis' can help eliminate the larvae. One product recommends mixing 1 to 2 teaspoons of product in a gallon of water to treat light infestations, and 1 to 2 tablespoons of product per gallon of water for heavy gnat infestations. Pour enough Bti solution into houseplant containers to thoroughly wet at least the top 1 inch of soil.