A gnat nest, constructed by fungus gnats, appears as a small, cotton-like mass, typically white or cream in color, and often found in moist, dark areas, such as under leaves, in compost piles, or around drains. The nest is composed of fine silk threads secreted by the larvae, along with other debris, like plant matter and soil particles. It provides shelter and protection for the developing larvae and pupae, and its close proximity to moisture ensures their survival.