Insectile aliens with a telepathic semi-hive mind bent on converting all other life forms into slave races.
Krrzxt stand about seven feet(2.13 meters) on average, with six being extremely short and eight being exceptionally tall. Take a digitigrade human body(fairly voluptuous female shape, but no nipples or visible genitalia) with grasping tarsal claws on the feet. Add an extra pair of arms. Make the skin firm and smooth, and slightly tougher than human skin. Bald head with antennae. The face is human, but with large, multifaceted black eyes. Twinned wings emerge from the back, and are capable of sustained flight. The 'abdomen' part of a wasp is represented by a sort of fat tail of similar shape ending in a vicious stinger.
Color is brilliant yellow striped and spotted with black.
They wear no clothes, but will have various harnesses of tools and weapons depending on their job within the Swarm.
One hell of a nasty stinger. They have genetically modified the venom glands in their bodies so that they are capable of delivering a fully stocked bar's worth of chemical cocktails, the most used of which is a powerful mind-control serum.
General arrays of space-age weapons. Blasters, lasers, etc. It's rumored that they have nonotech, but no one has been able to confirm this. Mostly because no one's ever successully escaped from a Hiveship.
They swarm. Seriously, it's what they do. They'll first send in a few scouts to determine the suitability of a particular world before simply overwhelming the local populace with sheer numbers(hence their common name).
They are intensely telepathic and telekinetic. While each member IS an individual, each Hiveship colony is constantly in mental contact with every other member at all times.
They have incredible difficulty pronouncing any language but their own(just as every other race finds theirs pretty much impossible). Therefore they must have devices that translate their buzzing speech into words for the benefit of others.
Being mentally isolated from their colony/siblings is extremely mentally damaging and may cause permanent, irreversible madness if prolonged.
Again, there are individual personalities, but each individual is very, very much more attuned to the greater needs of the Swarm/colony and the will of their Queen and through her, the Empress. So while they may express some individual quirks, talking with different Krzzxt can be an unnervingly similar experience.
The Swarm has been. The Swarm is. The Swarm endures and grows. The Swarm will always be.