The Harst were an interstellar insectoid civilization known to the Federation in the 23rd century.
History and specifics
Harst inhabited a region of space near systems containing the planets Elethia and Alsand. They had little contact with humanoid species, but were feared by Elethians and Alsandit.
In 2268, a conspiracy involving Elethian Queen Apathei and Alsandit Captain Tyren took advantage of those fears to disrupt the peace process between their worlds. Tyren claimed his ships were attacked twice by Harst ships. A trio of vessels attacked the starship USS Enterprise using an unusual gravity management field suggesting it had a non-humanoid crew, but all of the mysterious ships were later exposed as Alsandit ships participating in the conspiracy. (TOS - Star Trek: The Manga - Kakan ni Shinkou comic: "Scaean Gate")