Most species are black in color and very small (less than 1/16 inch) in size, although a few species may reach 1/4 inch long. Key identifying characteristics include long legs and long thin wings. See the Fungus Gnat image for detailed appearance.
To kill existing fungus gnats indoors, use Pyrethrin space sprays and pheromone traps or small, low profile Cento Fly Trap. To actually control and/or eliminate fungus gnat infestations in structures, the breeding sites of these flying pests must be addressed. Understanding the biology of fungus gnats is also of utmost importance if you wish to control the situation.
For those responsible for pest control in malls, corporate offices, doctor's office, hospitals or other commercial areas, fungus gnats can pose problems not encountered in residential areas. For gnat or fly elimination in commercial areas that are in public view, go to the Commercial Indoor Fly and Gnat Elimination page.
Locate all possible Fungus gnat breeding sites; these sites must be altered or eliminated. Because Fungus Gnats feed on fungus growing in moist organic matter and potting soil, the moisture in these areas must be greatly reduced or eliminated, if at all possible. When potting soil is allowed to dry between water applications, fungi are far less likely to grow. Without their food (fungus,) the fungus gnats cannot develop and mature into egg-laying adults.
These tiny pests belong to the families of flies called Fungivoridae and Sciaridae.
Adult Fungus Gnats prefer to lay their eggs in moist potting soil, which is why buildings containing potted plants or atriums. Soon after the eggs are laid, the larvae emerge to feed on fungus growing in damp potting soil. After feeding for a short period (little is actually known and been documented on their life cycle,) the larvae pupate. A few days after pupating, the adult Fungus gnats emerge to continue the cycle and increase the population.
Fungus Gnats are often first noticed flying to or around lights, both indoors and out. When adult Fungus Gnats are seen, begin inspecting the indoor areas for moisture problems. Although fungus grows in areas such as moist wood (the result of leaks or poor insulation) and poorly ventilated crawlspaces and attics, most infestations are associated with moist potting soil. Look for adult flies in areas where moisture problems have been observed or are suspected; fungus gnat eggs and larvae are more often not on the exposed surface of soil and are too small to see without good magnification.
Once you have successfully located one source, continue your inspection. There are usually several breeding sites in a building by the time adult flies have been become a nuisance. In many cases, Fungus Gnats are invading a building from outdoors. Finish your inspection by evaluating the soil around the building. Some flower beds and other landscaped areas are never allowed to dry properly between irrigation cycles. Sprinkler heads might be located too close together or need to be redirected. Make sure that these areas are not being watered too often or too much. Even with good irrigation practices, the soil in landscaped areas often retain moisture long enough to allow fungus to grow, which serves as another food source for fungus gnats. In these cases, raking the mulch and underlying soil will allow enough air circulation to increase drying times. Raking helps kill existing fungi, exposing them to light and air.
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