Mother Horta The mother Horta , born around 44773 BC , was the last of the Horta species of Janus VI until stardate 3196 in 2267 . Every 50 , 000 years every Horta dies except for one , who watches the eggs until they begin to hatch . When the Federation established a mining colony on the planet in the 2210s , the mother Horta initially tolerated the presence of the miners . But when automated machinery broke onto level 23 in 2267 , destroying thousands of Horta eggs in the Vault of Tomorrow , the mother began to fear for her children . She retaliated by destroying parts of the machinery with her powerfully corrosive acid , and when a maintenance engineer came to repair it , she killed him . Three months later , by stardate 3196 , she had killed over fifty people , including five guards ( such as Schmitter ) placed to stop her . Pergium production on the colony had been driven to a standstill . Colony administrative head Vanderberg summoned the for assistance , as the colonists could not locate or harm what they believed to be a mere animal . " Enterprise " science officer Spock deduced that the reason for this was because they were combating a silicon - based lifeform , which has been previously thought mere fantasy . He was able to modify the hand phasers of " Enterprise " personnel to function against silicon lifeforms . Spock and Captain James T . Kirk were able to harm the mother Horta after it killed a security officer , but it escaped through a freshly made tunnel . Shortly thereafter , Kirk encountered it once more , but wounded , the mother did not attack him . Spock was able to initiate a Vulcan mind meld with her , and using the knowledge she gleaned from the meld , she used acid to write " NO KILL I " in the cave floor . Spock revealed that the creature was actually a sentient creature protecting her children . The mother had stolen the main circulating pump from the colony ' s PXK pergium reactor , but in exchange for the return of the pump , Doctor Leonard McCoy was able to heal her phaser wound with thermal concrete . Once the situation was explained to the miners , they were suitably remorseful , but Spock negotiated an agreement between the Horta and the colonists via the mind meld . The colonists would leave the Horta eggs alone , and the Horta would use their abilities to assist in mining operations . Spock reported that the mother Horta had an extremely logical mind , and though she found the humanoid form displeasing to behold , she thought she could get used to it . Her favorite aspect was the pointed ears ; Spock could not bear to tell her that not everyone had them . ( ) Background information . The mother Horta was played by Janos Prohaska . Much of the information about the Horta ' s life cycle comes from the words of the Horta mother . Producer Robert Justman recalled how Prohaska , who had created the Horta costume himself , made the pitch for the role , " We made a " spec " " [ note : industry idiom for an unsolicited pitch without any guarantees ] " deal with Janos . If he came up with a really great creature for a script Gene Coon was writing , we ' d rent it and hire him to play the part . Janos was back within a week ' s time with his custom - designed creature . It was a large pancake - shaped glob of gook with a thickened raised center and fringe around its circumference . It sure didn ' t look like much . As Janos took the glob out of sight to put it on , Gene Coon raised an objection " Bob , why are wasting time with this ? " Suddenly , the blob skittered around the corner , making straight for us . Then it stopped , curiously , backed away , and rotated in place . The blob gathered itself up , quivered , made a whimsical up - and - down movement , grunted , and skittered away again & nadsh ; leaving behind a large , round white " egg " . Coon was dumbfounded . He watched the creature giving birth . And when the creature suddenly turned and scurried back to nuzzle its " child " , Gene was sold . " Great ! " he exclaimed , " It ' s perfect ! Just what we need . " Then he excitedly hastened back to his office to finish writing the script . Gene Coon ' s " The Devil in the Dark " became one of " Star Trek " s most famous episodes . And Janos Prohaska played his own creation , one of " Star Trek " s most famous creatures , the highly imaginative and custom - designed mother Horta . " ( " " , pp . 214 - 215 ) What neither Justman nor Coon had realized at the time however , was that Prohaska had actually already created the creature previously for " The Outer Limits " , first appearing in the final episode , and that he had only slightly modified the rubber costume with veins and the " fringe " for its " Star Trek " appearance . ( ) Titled " The Probe " ( with Peter Mark Richman ) , the " Outer Limits " 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 , the future Mrs . Horta was performing yeoman service as a giant cold germ threatening the hapless Earth people . ( " The World of Star Trek " , 3rd ed . , p . 74 )