Bloodrust

A dark red mold that grows close to the surface, this fungus is known not only to feed on iron, but also on blood of humanoids. While the fungus is known to leech iron out of arms or armor, it often takes decades before any noticeable affect occurs.
Bloodrust is mildly poisonous, and causes nausea (the poisoned condition) to anyone failing a Constitution Saving Throw, DC 15.