Size:
Approximately 1/16 to 1/4-inch in length.

Behavior:
Fungus gnats reproduce in moist, shady areas in decaying organic matter such as leaf litter or in homes where warm temperatures are maintained. Adults live about 7-10 days and deposit eggs on the moist soil surface or in soil cracks. Females can lay up to 100-300 eggs in batches of 2-3. Eggs hatch in 4-6 days; larvae feed for 12-14 days before emerging as adults. There are many overlapping generations throughout the year.

Habitat:
Fungus gnats occasionally become nuisance indoors when adults emerge in large numbers from potted plants or flower boxes containing damp soil rich in humus. Damage often occurs in greenhouses and plant beds. The larvae can injure the roots of bedding plants, African violets, carnations, geraniums, poinsettias and foliage plants. Some are serious pests in mushroom houses; larvae feed on fungi and decaying organic matter as well as living plant tissue, particularly root hairs and small feeder roots.

Fungus gnat infestation can cause brown scars to appear on the chewed roots. The underground parts of the stem may be injured and root hairs eaten off. Plant symptoms may appear as sudden wilting, loss of vigor, poor growth, yellowing and foliage loss. Fungus gnats may breed anywhere that suitable molds might grow.

A Fungus gnat infestation indoors may also mean a moisture problem is present. 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.

Interesting Fact:
Fungus gnats are attracted to light, so ultraviolet-light fly traps or “bug zappers” are capable of attracting and killing many adult fruit flies at night, as well as other winged pests.

Control:
Inspect plants carefully before purchase for signs of insect infestation. Always use sterile potting soil to prevent introduction of fungus gnats. Over-watering, water leaks and poor drainage can lead to concentrations of fungus gnats. Allowing the soil to dry as much as possible, without injury to the plants, is effective in killing many larvae. Remover all old plant debris in and around the home.

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