Fungus gnats like to feed on roots of the plants and organic matter. Adults and larvae live in moist, shady areas. The adults lay there eggs on top of the soil, near the base of the stem and takes about 4 days to hatch. The larvae will start by eating the root hairs of the plant then working their way up the plant, Fungus gnats like to eat organic matter so they will be stealing away nutrients from your plants,
Put potato slices on the surface of the soil. The larvae like it and will be drawn to it.. After about 4 to 5 days, remove the potato slices with the larvae.