The Fungus Gnat Fungus gnats are small, mosquito-looking flies that like decaying organic matter. There are several species within this group, all fairly similar in behavior. These gnats can be found around potted plants, pet cages, or rotting wood. When their habitat is disturbed, adults will fly out and hover around. Since they prefer decaying items, they aren't a large economic problem.
Adults are more of a nuisance than larvae, however the larvae do more damage.
Larvae can be a problem when they get into plants, eating the fungus and roots. Sometimes they can eat enough of the roots to cause the plant damage. In many cases, all that needs to be done is to dry out the source of moisture to inhibit fungus growth.