Mature gnats measure a mere 1/8 inch and live for about a week. During this time, females lay eggs in soil fissures. The resulting translucent, minute larvae feed largely on the assorted fungi growing in the potting soil, though they can also feed on fine roots and plant debris. In a few weeks, they pupate into adults within the soil and the cycle continues, with several generations occurring together at any given time.
If cutting back on water doesn't clear up the problem, repot the plant with new, sterile potting soil, gently removing as much of the old soil as possible without decimating the roots. Adult fungus gnats can also be trapped on yellow or blue sticky cards placed an inch or two above the soil surface.