How to Get Rid of Gnats

If you have an active gnat infestation, follow these guidelines for gnat control in your house.

Swatting away gnats from your face or food can be extremely annoying. They are attracted to body heat, water, and sweet or fruity scents. Gnats are one of the most common types of pesky flies that you'll find in your home or outside.

Gnats Are Often Mistaken For Other Small Flies

Gnats are often mistaken for other types of small flies found in homes.

Fruit flies, Drain flies, and Phorid flies resemble gnats to the naked eye, but gnats are much smaller under closer examination. Determining the breeding source will help you understand the type of fly you have. Fruit flies and Phorid flies breed from organic matter like fruits and vegetables, food spillage, and garbage. Drain flies breed in drains and sewer tanks and soil contaminated from sewage.

Gnats also breed in drains and are often are sourced from potted plants and fungi.

Gnat Identification and Inspection

Identification ( Where Are They Coming From ?)

  • Gnats: Gnats breed in all the sources listed above: drains, rotting fruits and vegetables,and trash cans. Fungus gnats are often spotted around potted plants or windows. They like to breed in very moist soil. These gnats are tiny flies with long legs and long thin wings. Looking closely, you will see vein patterns in their wings. Their eggs are semi-transparent, oval, smooth, and hardly visible. Their larvae (maggots) are white, with a shiny blackhead, and measure up to 1/4 inch long. In the soil, you can see silk-like cocoons, their pupae.
  • Fruit Flies : Fruit flies have bright red eyes with a round-like body; are common around rotting foods.
  • Drain Flies : Drain flies ( Moth flies) body colors are tan or a light gray color; their wings become dust when they are smashed. They are often seen around drains.
  • Fungus Gnat
    Fungus Gnat

    Gnat Inspection

    • Inspect soil of potted plants.
    • Look for adult gnats flying around the plants. This gnat swarm would indicate soil under the plants as a breeding source. It may be difficult to find or see larvae of gnats in soil.
    • Gnats may be entering the building from the outside if no planters or atrium areas are serving as breeding sources. Check the plants, soil, and organic matter near entry points like doors and windows.
    • Look for adult Fungus gnats flying around the plants outside as well.
    • Because fungus gnats are attracted to lights, occasionally, the exterior lighting on the building may be attracting fungus gnats from neighboring areas.
    • Also, look for water leaks or moisture problems inside such as water stains, swelled wall coverings, peeling paint, etc. If fungus is growing there, these gnats could be breeding there.
    • In new construction, moisture normally gets onto the lumber used to build houses. Occasionally, surface fungi will grow on wood inside wall voids, which don't dry out quickly. It is rare, but severe fungus gnat infestations have developed in new houses inside walls where fungi have grown. Remove the plates on wall outlets and attach tape over much of the opening to determine if this is occurring. Leave a gap between the tape pieces to allow air movement for the gnats to follow out of the void. If gnats are breeding in the walls, some will invariably become stuck to the tape. Try this on all wall openings in infested rooms if the walls are suspected as possible breeding sources.
    • Don't stop looking when one breeding the source has been found. In most cases, several breeding sources will be present.

    Steps To Get Rid Of Gnats

    Step 1: Locate and Eliminate Breeding Sources

    • Potted Plants or Outside Soil: If you have Gnats coming from any potted plants, locate the breeding source by a complete inspection and remove the soil or dry the soil.
    • Drains: Test to see if the gnats or drain flies are coming out of drains. A handy way to check to see if they are coming from drains, apply some clear tape over the top of the drain, with some holes in it for airflow. If the gnats or drain flies get stuck on the tape as they exit the drain, you know you have gnats or drain flies.
    • Fruits, Vegetable or Food Spillage: Eliminate decaying fruit/vegetable matter. Also check under refrigerators in the condensation pan.

    Step 2 : Use Traps, Enzyme Drain Products or BTI Products

    If you have gnats or other small flies that are coming from organic sources, you can use a Fruit Fly Trap or make your homemade traps.

    A. Homemade Traps
    1. Old Fashion Vinegar Trap: Place a little (1-2 tablespoons) apple cider vinegar with a teaspoon of sugar in a jar, with some dish soap. The cider vinegar will serve as an attractant, and the soap will keep them trapped and not able to fly out.
    2. Ripened Fruits: Don't throw away that ripe banana or apple. Fruit flies and gnats are attracted to ripened fruit. Put some of that ripened fruit in a bowl and cover it with plastic wrap with small holes poked into it. The flies will fly into the bowl but not escape.
    3. Almost Gone Red Wine: If you have fruit flies or gnats, they may be trapped to the bottom level of wine leftover in the bottle. They will crawl into the bottle and not be able to escape.
    B. Enzyme Drain Products
    • If you have gnats in the kitchen and you can not locate their breeding source ( food spillage or garbage) they may be coming from the drains. Apply the clear tape over the drains with punched-out holes to see if they are coming out of the drains.
    • Use an enzyme drain product like Invade Bio Drain and pour in the drains. Invade Bio Drain Treatment contains microbes and natural citrus oil in a thick formula to coat the sides of drains. Invade Bio Drain Treatment will eat through the residue and scum in drains, eliminating scum and odors in the drains. The oil in Invade Bio Drain Treatment smells like fresh oranges.
    • Unfortunately, bleach will not completely take out the debris collected in the drains.
    C. BTI Products (Bacillus thuringiensis israelensis)
    • Mosquito Bits not only will control mosquito populations, but will control Gnats
    • Mosquito Bits contain BTI (Bacillus thuringiensis israelensis) that will kill the Fungus Gnat larvae. Sprinkle or spread a few granules (not much is needed- see the label). Water will release it into the soil and kill the Fungi gnat larvae.

    Step 3 : Use Insecticides or Fly Lights

    Key Takeaway

    To eliminate gnats, you have to find and remove the breeding site. Often times this alone can eliminate the flies so quickly that no insecticides are needed.

    How To Prevent Gnats

    • Don't Over Water Plants : When plants are over watered, increasing moisture, it causes conditions for Fungus Gnats to breed.
    • Allow Enough Time Between Watering Outside : If landscaped areas are not allowed to dry enough between watering periods, fungi can grow.
      • Even without over watering, landscaped areas may retain moisture long enough to permit the fungus to grow, causing conditions for breeding fungus gnats.
      • Raking the soil or mulch will killing the existing fungi as it is exposed to air and light.
    • Repair Water Leaks : Moisture problems from water leaks will cause increased fungal growth to encourage fungus gnat growth.
    • Proper Ventilation : Discourage fungi growth with proper ventilation.

    Fungus Gnats Biology and Habits

    Gnats reproduce in decaying organic matter that is moist and shaded. The larvae feed on fungus growing in the soil and moist organic matter. The larvae will also feed on live plant tissue, especially in root hairs and small roots. Damage from these Gnats occurs most often in greenhouses or plant beds.

    The life cycle is about four weeks, with continuous reproduction in homes or greenhouses where warm temperatures are maintained. Adults live about 7 to 10 days and deposit eggs on the moist soil surface or soil cracks.

    Females lay up to 100 to 300 eggs in batches of 2 to 30 each in decaying organic matter. Eggs hatch in 4 to 6 days; larvae feed for 12 to 14 days. The pupal stage is about 5 to 6 days. There are many overlapping generations throughout the year.

    Adult Gnats are very attracted to light and can be found flying in windows and around lamps.

    Written by our resident pest control expert Ken Martin.