The Zerith were a race of six-foot tall praying mantises, that looked as if they were made of glass. They appeared to be feminine, referring only to their "sisters" with no mention made of males in the species.
The Zerith existed in the same system as the Vilal and went to war with them, refusing to share the system. The Zerith possessed transmat technology, as well as the ability to access the time vortex and track their enemies. Using a giant psychic-projection of himself, and invoking his Time Lord authority, the Sixth Doctor forced the Zerith and the Vilal to end their war in Vienna in 1948. (AUDIO: Quicksilver)