If conditions are especially moist and fungus gnats are abundant, you may notice tiny, narrow slime trails on soil surfaces that resemble slug or snail trails but are much smaller. Found outdoors as well, fungus gnats breed in decaying plant matter, leaf mold, organic mulch, grass clippings, compost and fungi. These persistent gnats live short, prolific lives. An adult fungus gnat lays up to 200 eggs during the one week it spends as an adult winged gnat. The adult then dies.
Legless larvae hatch out in about four days.
After two weeks of feeding, larvae spend about three to four days as pupae before emerging as the next generation of adults. Most fungus gnats are merely annoying and cause relatively little damage to plants. But several species of fungus gnat larvae feed on roots, causing damage to African violets and other houseplants. Others burrow into stems and leaves. Fungus gnat-damaged plants may show signs of wilting.