Mites are small, flesh-eating insects which inhabit an island in the Waterway. They are first mentioned in Gregor and the Prophecy of Bane when Gregor and his friends encounter the island while traversing the Waterway. Ares and Pandora attempt to feed upon the mites, only to have their prey turn upon them. Perdita is eaten alive, but Ares submerges himself underwater at Gregor's suggestion, and escapes with multiple bites.
In Gregor and the Curse of the Warmbloods, it is speculated that the mites might have been the initial carriers of the plague since Ares was one of the first to fall ill. This theory was later refuted.
In Gregor and the Code of Claw, Ripred finds himself fighting enemy rats in a tunnel during the final battle in an effort to protect Boots and Lizzie. Unbeknownst to all, the tunnel emerges at the Waterway, and Ripred and his opponents find themselves surrounded by the mites. Though all are presumed dead when the skeletons of several rats are found in the tunnel, it is later revealed that Ripred saved himself by taking refuge under the corpse of one of his adversaries, a ploy which bought him enough time to flee.