Erechthias simulans is a fungus moth species (family Tineidae). It is here considered to belong to the somewhat controversial type genus of its subfamily Erechthiinae, though even fairly recently some authors have proposed to retain other genera such as Decadarchis separate from Erechthias. Decadarchis, with E. simulans as type species (under the obsolete name Decadarchis melanastra), would in fact contain this moth and its closest relatives, regardless whether it is recognized as full genus or as subgenus. These relatives are generally held to be a group of mainly Polynesian species. E. simulans has also been mistaken for a species of the closely related genus Comodica; while the delimitation of this versus Erechthias/Decadarchis is not universally agreed upon, E. simulans is not included