Black fungus / Mucormycosis is a rare but dangerous infection. It’s caused by a group of molds known as Mucormycetes. These fungi can be found in decaying leaves, compost piles, and rotten wood. Molds require moisture and decaying organic (living) material to thrive. Mucormycetes release large numbers of spores that can go into the air. Infections occur more frequently in the summer and fall than in the winter and spring.