Devidians []

Devidians in their true form
These individuals were observed by Data when he transported down to Devidia II. They lived out of phase and Data used a phase discriminator to make visual contact with them. They were two and three meters in height, had no eyes and possessed an orifice that resembled a mouth. They ingested Human neural energy as their nourishment. (TNG: "Time's Arrow", "Time's Arrow, Part II")
Female in Human form []
This Devidian took female Human form and traveled back to 19th century San Francisco in order to obtain Human neural energy, which was the Devidian's nourishment. She and her male counterpart acquired this energy by draining the subject of their neural energy, killing the subject. (TNG: "Time's Arrow", "Time's Arrow, Part II")
Male in Human form []
This Devidian took a male Human form and traveled back to 19th century San Francisco in order to prey on Humans. Human neural energy was the Devidians' nourishment. They acquired this energy by draining the subject of their neural energy, killing the subject. (TNG: "Time's Arrow", "Time's Arrow, Part II")