Homeowners often find many types of nuisance pests indoors, including some that are, or resemble, little flies. Fungus gnats are small insects that look like flies and often swarm indoors. These pests live in the potting soil of houseplants and can become a nuisance if left untreated. Eliminating the breeding site indoors is the most effective means of fungus gnat control.
Fungus gnats are also known as darkwinged fungus gnats and are common indoor pests. These insects often fly inside from outdoors or live in the potting soil of indoor plants. Adult fungus gnats measure about 2.5mm in length and are grey or black. These pests closely resemble mosquitoes but have longer legs. Fungus gnat larvae live in potting soil and look like white, grublike worms.
Fungus gnats feed on the decaying matter in potting soil of indoor plants. The larvae feeds on plant roots, causing houseplants to appear yellow, wilt or have reduced vigour. Fungus gnats do not bite animals or humans and are generally harmless, but they can become a nuisance for homeowners. Fungus gnats tend to gravitate toward natural light and are often found flying on windowsills. Moving your potted plants often causes these insects to swarm, but they settle back on the plants quickly.
Removing the breeding source of fungus gnats is the best form of control. Discard a plant with heavy fungus gnat infestation. Placing sticky traps just above plants with light infestations of fungus gnats may help to keep them under control. Allow the potting soil of your houseplant to dry completely before watering because fungus gnats breed in moisture. Dry soil also can kill many fungus gnat larvae. Inspect a plant you placed outdoors for fungus gnats before bringing it inside your home.
A wide variety of insecticides available at garden centres include labels stating they control flying pests or gnats. Always follow the directions on an insecticide's label. Repeat applications of an insecticide may be necessary to keep fungus gnats at bay. Use chemical control products in conjunction with cultural control methods for best results.