The Common Fungus Moth has a wingspan of 1.25 inches. The forewing ground coloring is pale yellow, but it is mostly obscured by extensive dark brown and black mottling. The basal and antemedial lines are scalloped. A broad black band crosses the wing in the median area. A pale band crosses the wing just inside the postmedial line, which is an indistinct series of pale dots. The hindwing is similar but lacks the basal and antemedial lines. The caterpillar is variably white to brown to almost black with sparse black hairs sprouting from yellowish warts. The larva grows to 1 inch.