These small (about ¼ inch long), black flies are commonly found around decaying vegetation. They have large wings and long antennae, but they are weak flyers and do not move far from the breeding site. 

(Sciara spp.) In the household, fungus gnats are usually found around potted plants, because both the adult fly and the larvae require a humid environment. The larvae can complete their development by feeding on the wet and decaying organic matter in potting soil. The lifecycle may be completed in about 10 days, and the adults may live about 2 weeks. The adults usually remain close to the breeding site. 

Infestations of fungus gnats usually occur during the winter months when houseplants may be over-watered and the moist soil provides a breeding site for the larvae. Control can be achieved by permitting the potting soil to completely dry between watering, this will kill the fungus gnat larvae.