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Devidians are a dangerous alien species from Star Trek whose need for neural energy makes them one of relatively few species in the universe who are unable to co-exist with current day humanity.
Devidians were a vaguely humanoid, shapeshifting species native to Devidia II. Their physical characteristics composed of being between 2 and 3 meters in height; they had no apparent eyes but they possessed an orifice on what most humanoids would call their forehead, that resembled a mouth. They lived out of phase with most other lifeforms with a phase variance of 0.004. They also possessed the ability to travel through time.
Devidians' only useful form of nourishment was neural energy. They acquired this energy by draining the subject of their neural energy, killing the subject. They preyed on Humans from 19th century San Francisco using the cholera epidemic at the time as a cover for their murders.
In 2369, the USS Enterprise-D fired modified photon torpedoes on the Devidians' cavern habitat to prevent them from further incursions.
First Splinter Timeline
In 2373 the USS Enterprise-E was able to successfully prevent the Borg from altering the timeline by traveling back to the mid 21st century. As the Enterprise returned to the 24th century, the Borg on the assimilated Earth where the Borg had sucessfully altered time fired a temporal beam on the ship, hoping to remove the Enterprise from history. The beam failed to remove the Enterprise from history but created two alternate timelines. One in which the Borg were still in control of Earth after interfering in human history, and a second timeline that branched off from the prime reality upon the Enterprise returning to the 24th century. Traveling through time and between universes from this timeline created new timelines and alternate realities.
Because of this temporal manipulation, the Devidians of the First Splinter timeline discovered alternate timelines and that by collapsing timelines they could absorb all the neural energy from the collapsed timelines. They began destroying timelines to obtain neural energy, and eventually began collapsing what would come to be called the First Splinter Timeline. Discovering the truth of their reality and the threat the Devidians posed to all universes and timelines, Starfleet personnel fought back to stop the Devidians from completing their temporal acopalypse, and to initiate a temporal recursion that would erase the First Splinter Timeline and the Borg timeline from history.
In his last moments of his existence, the Picard of this timeline was able to initiate the temporal recursion. He not only ensured that the timelines were never created, but that the Devidians did not discover how to collapse timelines and absorb neural energy from collapsed timelines. In his last moments of existence, Picard was satisfied that he had saved the prime reality and that it would be able to continue on.
Other Media
In Star Trek Online the Devidians have found a way to return to the corporeal universe and have begun to feast on other species, most notably the Cardassians - they plan a mass invasion of the corporeal universe in order to drain the neural energy of other lifeforms, leading to a great many deaths and a five-part storyarc.
Trivia
The Star Trek: Coda novel series was written as a way of establishing that the novelverse was an alternate reality that branched off from the prime reality following the events of First Contact as Star Trek: Picard and Lower Decks showed galactic history unfolded quite differently than the continuty of the novelverse, and to conclude the novelverse in a way that gave closure to the novel series while avoiding the abruptness of the rebranding of the Star Wars expanded universe to the Legends continuity. In the course of writing the series, the authors decided to make the Devidians the overarching antagonists of the series who had gone from temporal carrion eaters to temporal apex predators.
