Rock Demons were predatorial creatures dwelling at the bottom of a deep fissure in Screetown. The Guardians of Night would feed Librarian Knights to them. In Vox, the Rock Demons escaped the Rock Demons Ravine through a tunnel dug by the Guardians of Night. Following the scents of Magda Burlix and Xanth Filatine, the Rock Demons found their way into The Great Storm Chamber Library during the invasion of the goblins and shrykes. Upon arrival, the Rock Demons devoured both armies.