In the mirror universe, the Deltans were a subject species of the Terran Empire. As of the 2260s and 2270s, Deltans could be found serving on board Imperial Starfleet vessels. Lieutenant Ilia was one such Deltan, who served aboard the ISS Enterprise under the command of Admiral Spock. It was known by some in Starfleet that Deltans possessed rudimentary telepathic abilities. However, these abilities were not powerful enough to warrant their extermination by the Empire. (TOS - Mirror Universe novel: The Sorrows of Empire)