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. Gnat damage may weaken plants and make them susceptible to root rots. But they aren't all bad.