Theela's species
Theela's species was a technologically advanced humanoid race that originated from Theela's homeworld.

History 
At some point, before the early 22nd century, this species' homeworld began to die, forcing its inhabitants to emigrate to a new world. They group eventually settled on the second planet of the Taurean system, where they built a  and numerous other architectural wonders surrounding it. Unfortunately, what these settlers did not know was that the planet naturally drained humanoid energy.

After living in the Taurean system for some time, the female's bodies were able to adapt and develop a glandular secretion that enabled them to survive, functioning at an unusual psychokinesis level. These adaptations allowed them to manipulate certain areas of the males' brains, and influence their emotional senses. This ultimately drained the men, causing them to weaken and die.

The women learned that, to survive, they must revitalize their bodies every 27.346 star years, making them eternal prisoners of the planet, capable of neither aging, dying, nor bearing children. Once all the men on their planet had died, they resorted to revitalizing themselves by means of summoning male crew members of starships, from as far as twenty light years away, through the use of their opto-aud.

Beginning as early as 2119, they began luring starships from the Earth-Federation, as well as the Klingon and Romulan Empires. Once lured to the planet, the men were captured and forced to wear headbands with polarized conductors that drained energy from humanoids.

In 2269, the  was investigating several disappearances within range of the Taurean system when the starship's male crew members fell victim to the women's summons. After the women were defeated by Lieutenant Uhura and the female crew members of the Enterprise, Theela, their Head Female, agreed to destroy their opto-aud in exchange to be relocated to another system, by a Federation starship crewed by women, on the first suitable planet. Once relocated, according to Dr. McCoy, these females would become "normal" once again, after only a few months. ()

People 
 List of Theela's species

Background information 
The ization of "The Lorelei Signal" (as written by Alan Dean Foster and published in Star Trek Log 2) describes the female inhabitants as being "about two and a half meters tall" and repeatedly refers to them as "giantesses." This is not evident in the episode.

The species was not named on screen, nor received an entry under any name at StarTrek.com. However, they were described as Taureans in passing on the entry for Uhura on the site.  The name was probably not their original one, as they did not originate on the Taurean system planet where the Enterprise found them.

Unnamed species