There are races that live in balance with their ecosystem, and then there are those that consume it, devouring everything in mindless expansion. Such is the case with the Swarm.
Originally called the kucharn, the race now called the Swarm evolved as a series of hives, each colony a collective consciousness in which the individual bug-like components acted as drones, without agency of their own. Efficient, voracious predators, each worshiping its own patron deity, the hives competed constantly with each other, until one learned the trick of subsuming another colony’s intelligence into its own. This new collective quickly overwhelmed the others, and before long it had stripped its birth planet bare with its reflexive hunger. This might have been the end of the Swarm, had it not come to understand the principles of spaceflight. Tearing itself apart into component pieces, rising above its all- consuming hunger to twist its own genome, it crafted biological warships capable of carrying it through the stars, descending on world after world to devour, destroy, and absorb.
The Swarm’s millions of individual units remain divided into subcolonies with a certain degree of autonomy, but like the drones themselves, their decisions are more akin to complex programmed reflexes than true thought, constantly overridden by the directives of the master identity. While they’re capable of operating independently when sent out on scouting missions, both individuals and entire subcolonies are subsumed into the gestalt when they return within telepathic range of the hive. The overarching Swarm consciousness—while capable of nigh-unimaginable data processing, leaps of induction, and even the ability to slowly modify its own biology to create powerful weapons—remains fundamentally unreasonable due to an overwhelming, instinctive impulse to blindly expand and devour. Attempts to negotiate with the Swarm always fail, and only massive force can deter it from descending on a world and stripping it of biological material before moving on. In its view, every other organism in the universe represents a threat, and all threats must be destroyed.
Strange, then, that a freak mutation should lead one subcolony to split off and flee its ravager-parent, becoming the peace-loving shirrens. While all races rightly fear the arrival of the Swarm in their space, shirrens find the idea of being once more subsumed into the Swarm’s hive mind even worse than the prospect of annihilation.