Fungus gnats or sciarids are small (mostly 2 mm in length), dark coloured gnats, the larvae of which feed on decaying organic matter or fungi in the soil. While constructively participating in the biological material cycle in nature, they can be a nuisance in indoor plants and cause significant damage in plant propagation houses. The milky-white larvae are slender and grow up to 5 mm. Fungus gnats proliferate very well at high soil moisture and.