The insectoids. They're so... different
from anything that you usually see in ST.
They also break the typecasting of insectoid aliens in sci-fi by being actual normal individual sentients. About 90% of the time when insectoid aliens turn up in sci-fi, they are depicted as a hive society, with big dumb drones by the bajillion, with a central controlling overmind / queen type thing that has more intelligence to it. It gets tired after a while.