In Book V of The Return of the King, in "The Black Gate Opens," as the Captains approach the Gate, Tolkien makes this statement (phrase in question bolded by me):
North amid their noisome pits lay the first of the great heaps and hills of slag and broken rock and blasted earth, the vomit of the maggot-folk of Mordor; but south and now near loomed the great rampart of Cirith Gorgor, and the Black Gate amidmost, and the two Towers of the Teeth tall and dark upon either side.
North of the Black Gate is actually outside Mordor, but obviously the landscape north of it was affected by these "maggot-folk of Mordor." The question I have specifically is if "maggot-folk" is merely a general, descriptive, collective term referring to all the various "peoples" of Mordor (orcs, trolls, evil men, etc.) or is there some evidence in other writing that Tolkien is here making an identification of a specific people group that were part of Mordor who terraformed the landscape in such a destructive way?