Species M-113, or salt vampire, was a sentient humanoid species native to planet M-113 in the galaxy's Beta Quadrant. With the death of the last specimen on M-113, the Federation believed the salt vampires extinct. (TOS episode: "The Man Trap")
The creatures were a highly intelligent species that used telepathy to draw in prey by extracting an image from their minds and taking that form. Once the prey was completely drawn they then used to draw sodium chloride - salt - from a prey's body through suckers that were on the creatures hands. They also possessed tremendous strength and an ability to survive several phaser shots at short range. (TOS episode: "The Man Trap")
A group of M-113 was organized by size and age, with hatchlings being the youngest, smallest, and weakest creatures. Older creatures, ranked from weakest to strongest, included the adult, Beta, and Alpha. (STO - New Romulus mission: "Mine Trap")
At the height of their existence, there were millions of creatures that roamed around the planet in a similar fashion to the buffalo of Earth. However, by the 2260s only a single specimen remained. In 2265, this lone creature encountered Professor Robert Crater and his wife, Nancy. During this encounter, the creature killed Nancy and took her form to stop Professor Crater from killing it. (TOS episode: "The Man Trap")
A year later, the USS Enterprise arrived to conduct medical examinations of the Craters. By this time, the amount of salt contained in the Craters' encampment drove the creature's hunger to murder Crewman Scott Darnell on the surface of M-113; as Nancy Crater, it blamed Darnell's death on ingestion of a Borgia plant. The creature then went on to murder Crewmen Sturgeon and Green when a further landing party returned to the surface.
Impersonating Crewman Green, it returned to the Enterprise, where chance saved Yeoman Janice Rand from becoming its next victim. It followed her when she brought Hikaru Sulu his dinner in the botanical garden, and might have murdered both officers except that Beauregard, a Weeper plant, being studied by Sulu, became agitated and scared it off.
Around this time, Captain Kirk and Commander Spock found Professor Crater on the surface of M-113, and returned to the ship with him. The creature, then impersonating Doctor Leonard H. McCoy, sat in on a staff meeting at which it learned that Crater knew how to identify it. Before Crater could reveal how this might be done, the creature murdered him, attempted to feed off Spock, and fled to McCoy's quarters, once again as Nancy. Kirk found it there, and attempted to lure it to him with salt. In the resulting scuffle, it overpowered Kirk and began to feed on him. It wasn't until the creature dropped its telepathic projection, and Kirk began to scream from the pain of salt extraction, that McCoy was able to shoot and kill the creature. (TOS episode: "The Man Trap")
In 2409, after a series of mysterious deaths at the Romulan mining colony on Hfihar, creatures similar to the M-113 creature were sighted in large numbers on the planet. A combined force of Starfleet and Klingon officers were able to hold them at bay long enough for the civilian population of the colony to be evacuated to safety.
Scientists observing the attacks noted that the original M-113 creature would not have been able to sustain itself on Romulan copper-based blood, and speculated that the Hfihar creatures had been genetically engineered as a weapon for use against Vulcanoid beings. Survivors also speculated that the appearance of the creatures had some connection to the Tal Shiar base known to exist in the system. (STO - New Romulus mission: "Mine Trap")
In an alternate timeline affected by the temporal anomaly crisis, a Federation team led by a version of Pavel Chekov found Species M-113 forming a peaceful civilization on the planet Meridian in the Gamma Quadrant. Working with the Romulan Star Empire and Ferengi Alliance, the team armed and protected Species M-113 from the crazed Garth of Izar, who thought Meridian to be his "New Eden". (ST video game: Star Trek Timelines: Galaxy Event: "New Eden")
- Species M-113 article at Memory Alpha, the wiki for canon Star Trek.
- Species_M—113 article at The Star Trek Online Wiki.