Horta physiology was very different from the carbon-based norm more commonly found in the galaxy. Horta were difficult to detect with tricorders, and were invulnerable to type 1 phasers, though they could be injured with an adjusted type 2 phaser. They fed on rock, and thus they were nourished just by tunneling. Horta tunneled through rock like most humanoids walked through air, moving with the aid of an extremely corrosive acid. They left perfectly round tunnels in their wake. This acid was so corrosive that it only left fragments of bone and teeth if used on a Human. Although Hortas did not evolve in an oxygen environment, they seemed able to exist in it for extended periods of time.
The Horta species possessed (as compared to carbon-based lifeforms) an unusually long life span. Every fifty thousand years, all of the Horta died out except for one, the so-called mother Horta, who then watched the eggs until they hatched, and mothered and protected them. Horta eggs were spherical in shape, and they seemed to mostly consist of silicon, aside from a few trace elements. They were stored in the Vault of Tomorrow in the Chamber of the Ages.
It was in the midst of one of these temporary phases of extinction that the Federation colonized Janus VI in the 2210s. The mother Horta tolerated the Federation presence up until the miners established a new, lower level in 2267, where they first encountered Horta eggs. Thinking them nothing more than balls of useless silicon, the miners' automated equipment destroyed thousands of them. The mother Horta defended her children by carrying out actions of sabotage and murder against the Janus VI colony.
It was only when Commander Spock of the USS Enterprise mind-melded with the mother Horta that he was able to determine that the Horta was actually an intelligent lifeform. In fact, before the discovery of the Horta, silicon-based life had been thought a fantasy by Federation scientists.
The mother Horta reached an accord with the miners, who were distressed at the destruction they had caused. The miners would leave the Horta alone on the lower levels once they began hatching, while the Horta would use their abilities to locate and construct access to choice mineral deposits for the miners. Just as the Enterprise departed the planet, the first baby Horta hatched and began tunneling rapidly. (TOS: "The Devil in the Dark")
"NO KILL I"
- - Horta Mother
"I'm a doctor, not a bricklayer!"
- - Dr. McCoy
The German word "Hort" (male gender, der Hort) means hoard (as in hoard of treasure or supplies). In some regional dialects, the word's meaning is extended to include "all-day nursery" – a place where you "hoard" children, fitting the role the Horta has.
The Horta was played by Janos Prohaska. The "suit" for the Horta, also with Prohaska inside, first appeared in the final episode of the original ABC series The Outer Limits. Titled "The Probe" (with Peter Mark Richman), the episode's storyline was about survivors of a plane crash in the Pacific waking up to find themselves (and their life raft) on the floor of an alien spacecraft sent to collect terrestrial lifeforms. In this episode, broadcast in January 1965, the future Mrs. Horta was performing yeoman service as a giant cold germ threatening the hapless Earth people. The same costume, which Prohaska made from rubber, inspired Gene L. Coon to write "The Devil in the Dark", thereby creating the Horta. (The World of Star Trek, 3rd ed., p. 74)
A Horta was referenced in the first-draft script for "In Thy Image" – the story that gradually developed into Star Trek: The Motion Picture – in which Kirk reminded Dr. McCoy, now a veterinarian, of the Horta having been "patched up" by McCoy using silicone cement. (Star Trek Phase II: The Lost Series, p. 125)
Two days before filming of the Federation Council scenes in Star Trek IV: The Voyage Home, it was requested that one of the aliens present in the setting be a Horta ambassador. As notice of the request was given so soon before the scenes were shot, however, the creation of a Horta in time for filming was an impossibility. Thus, the Horta failed to make an appearance in the film. (text commentary, Star Trek IV: The Voyage Home (Special Edition) DVD)
Some new CGI visual effects were created for the Horta, in the remastered edition of "The Devil in the Dark", for the 40th anniversary of the original series. Notably, the Horta emerging/tunneling through a particular rock face, when Captain Kirk encountered the Horta mother on his own, was a combination of new and original footage.
Although there is no current canon reason to believe the Horta ever left Janus VI, in several non-canon novels and comic books by Diane Duane, there is a Horta crew member on the Enterprise, Ensign Naraht – in particular, Naraht plays a critical role in The Romulan Way. The novel Articles of the Federation, by Keith R.A. DeCandido, has the Horta as members of the Federation as of 2380 and are represented by one Councilor Sanaht. Further appearances include the Greg Cox and John Gregory Betancourt's DS9 novel, Devil in the Sky. Hortas were also mentioned in The Lost Years.
In the TNG novel Dyson Sphere, it is revealed that Starfleet has starships crewed entirely by Horta. These ships are of standard design, with nearly all amenities removed, and are filled with solid stone, which the Horta can reshape as they see fit.
In the MMORPG Star Trek Online, in the mission "Mine Enemy", a Horta kills Tal Shiar officers and burns the words "NO KILL I, NO KILL I" into a cave floor with acid. If the player observes this, he or she will get the accolade: NO KILL I. The mission reward is a Horta hatchling pet that follows the player when activated from the inventory. Also, during the one-year anniversary, Q visited and the Horta is one of many creatures that players were turned into for three minutes when they offended him.