Devidian

The Devidians are a sapient race of humanoids from the planet Devidia II, located in the Marrab Sector of the galaxy. They kill their victims by feeding off their neural energy.

Biology
Devidians are humanoids, ranging from two to three meters in height, and silver-grey in color. They have no visible eyes or ears, but possess a single orifice on their foreheads which is used to ingest "fragments" of neural energy taken from their victims. They're also capable of altering their appearance to look Human.

Devidians are among the few life forms which can withstand triolic waves, a form of energy considered hazardous for most other species. They have been described as possessing microcentrum cell membranes, which make them immune to the degenerative effect of the waves, and also allow them to shapeshift.

In addition to their shapeshifting abilities, the Devidians and other life forms from their homeworld are also capable of shifting out of phase with reality, thus becoming invisible and essentially undetectable.

Culture and society
Devidian technology is largely based on triolic waves. They also make use of a non-sapient creature described only as an Ophidian, which is capable of generating localized distortions in the fabric of spacetime.

By using a device which can focus the distortions provoked by the Ophidian, the Devidians can create temporal vortexes and use it to access other planets and eras containing life forms which they can easily prey upon. They created a vortex linking a cave in 24th century Devidia II to another one in 19th century Earth, a time period plagued with some epidemic diseases and in which mysterious disappearances of certain people wouldn't be as notable as in later centuries.

Appearances

 * Star Trek: The Next Generation
 * s05e26 - "Time's Arrow" (1992)
 * s06e01 - "Time's Arrow, Part II" (1992)