Gnat Facts, Identification, and Control in New York, New Jersey, and Connecticut
Scientific Order: Diptera
Common Family: Six of the seven families within the superfamily Sciaroidea, particularly the family Sciaridae
Size: Adults of different species may be as small as 2 millimeters, or as large as ½ an inch (12.7 millimeters).
Color: Black, grey, or even dark orange-yellow with translucent grey or clear wings. The identifiable mark on most species is the Y-shaped, vein-like pattern in their wings.
Signs of Infestation
Adult gnats are attracted to light sources, especially at night. Look for swarms of black gnats around indoor and outdoor lights at night, especially in warm or humid areas of the house.
Fungus gnat larvae burrow into the soil to hide and feed more effectively. Indoors, gnats will lay eggs in potted plant soil and then rest on plants nearby. You may find larvae in the soil around areas where you see adult gnats.
Treatment and Prevention
Preventing fungal growth is the most important way to prevent fungus gnat infestation. Carefully control humidity in your building. Fix plumbing leaks, runoff, excess condensation, drafts, and other sources of excess moisture.
Dispose of decaying organic matter quickly and efficiently. Take out your garbage every night, and clean your dumpsters regularly. Maintain your indoor plants diligently and remove them if they die or become infested with gnats.
Behavior and Diet
Fungus gnats are attracted to fungi such as mold, decaying matter, mushrooms, and sources of moisture. Larvae feed on the root systems of plants, interfering with the plant's ability to absorb water and nutrients.
Adult fungus gnats are attracted to light and often swarm around indoor light sources. They're especially active during warm, moist autumn weather, when they can infest wet leaf piles during the day.
Reproduction and Life Cycle
Fungus gnats have short life spans and grow quickly. Their entire life cycle process can complete in 20 to 28 days depending on the temperature of the growth environment. The fungus gnat’s life cycle is broken up into four distinct stages: egg, larvae, pupa, and adult.
A single female fungus gnat can lay up to 300 eggs at a time and can lay up to 1000 eggs in her lifetime. Eggs hatch quickly. Larvae feed continuously and require considerable moisture and energy to pupate. After around 10 days, larvae pupate. After about 7 days pupating, they emerge fully grown.
- Fungus gnats don't "attack" or bite people, so they're primarily considered a nuisance pest.
- In large enough numbers, fungus gnats can inflict significant root damage to the plants they feed on. This damage is particularly common in greenhouses.
- Unlike other common pest flies, fungus gnats are very poor fliers. Adults can only sustain flight for short periods of time and don't move around much indoors.
University of Florida Department of Entomology & Nematology darkwinged fungus gnats “Featured Creatures” page
American Orchid Society’s Orchid Pests and Diseases: Fungus Gnats page, by Paul J. Johnson, Ph. D.
University of Vermont Extension Department of Plant and Soil Science’s “Fungus Gnats” page by G.R. Nielsen