Fuligo septica occurs as slimy to crust-like sheets or cushion-like iregular masses on stumps, logs, living plants, and wood mulches in landscapes in the warmer months. This slime mold first appears as a white to yellow slimy mass. The 'flesh' transforms into a crusty, cake-like mass of darker and variable color. The brittle
crust easily breaks away to reveal a dull-black spore mass.
Although many slime mould species fruit on wood they do not form a penetrating and absorptive mass of hyphae in the wood substrate. Rather, slime molds form structures called plasmodia which are naked (i.e., without cell walls) masses of protoplasm which can move and engulf particles of food in an amoeboid manner. Slime mould plasmodia creep about over the surfaces of materials, engulfing bacteria, spores of fungi and plants, protozoa, and particles of nonliving organic matter. At some point, plasmodia convert into spore-bearing structures.
In Fuligo, the plasmodium converts into a cushion-shaped mass of spores enclosed by an outer wall called a peridium. This structure is called an aethalium. Fuligo septica produces the largest spore-producing structure of any known slime mould.