Tholian

Tholian Race

Little is known about the Tholian race. No member of this race has ever been seen in person by a United Fedaration of Planets representative, and almost nothing is known about their physical capabilities. What limited information exists are educated guesses based on starship-to-starship encounters, viewscreen observation, and very limited data. Tholians are assumed to be crystalline in structure, requiring high temperatures to survive; they are punctual, precise, extremely suspicious, and unwilling to make face-to-face contact.

For a story of one of the first encounters with the Tholians: http://en.wikipedia.org/wiki/Tholian_web