The Zerg Swarm are a race of fictional insectoids and the overriding antagonists of the StarCraft series. Operating as a hive mind, the Zerg strive for genetic perfection by assimilating “worthy” races into their own, creating numerous different strains of Zerg. Unlike the Protoss and the Terrans, the Zerg do not use technology, instead using assimilation of other species and directed mutation to develop traits to match such technology. As with the other two primary races, the Zerg are the subject of a full campaign in each of the series’ real-time strategy video games. Zerg units are designed to be cheap and fast to produce, encouraging players to overwhelm their opponents with sheer numbers. Since the release of StarCraft the Zerg have become a video gaming icon, described by PC Gamer UK as “the best race in strategy history”. The phrase “zerging” has entered video gaming jargon to describe using many low-cost and weak units to overwhelm an enemy.
The Zerg are a collective consciousness of a variety of different races assimilated into the Zerg genome. The Zerg are originally commanded by the Zerg Overmind, a manifestation of this hive mind, and under the Overmind’s control the Zerg strived for genetic perfection by assimilating the favourable traits of other species. After a species has been assimilated into the Swarm, it is mutated towards a different function within its hierarchy, from being a hive worker to a warrior strain. StarCraft‘s manual notes that some species bear little resemblence to their original forms after just a short time into assimilation. The Overmind controls the Swarm through secondary agents called cerebrates. Cerebrates command an individual brood of Zerg, each with a distinct tactical role within the hierarchy. Cerebrates further devolve power through the use of overlords for battlefield direction and queens for hive overwatch.
The vast majority of the Zerg do not have any free will as they are genetically forced to obey the commands of those further up the Zerg hierarchy, although they are sufficiently intelligent to form strategies and work as a team on the battlefield. Despite this, the average Zerg has no sense of self preservation. Along with the Overmind the cerebrates are the only Zerg with full sapience, each with its own personality and methods, although they too are genetically incapable of disobeying the Overmind. The Overmind also possesses the ability to reincarnate its cerebrates should their bodies be killed, although Protoss dark templar energies are capable of disrupting this process. If a cerebrate is completely dead and cannot be reincarnated, the Overmind loses control of the cerebrate’s brood, causing it to mindlessly rampage and attack anything. As a result of the Overmind’s death in StarCraft and the subsequent destruction of a new Overmind in Brood War, Blizzard Entertainment’s Chris Metzen revealed that the surviving cerebrates perish as they are genetically incapable of surviving without their master, leaving the infested Terran and prize of the Overmind, Sarah Kerrigan, in complete control over the Swarm.
The backstory for the series describes the original Zerg as small larvae, the “most insignificant lifeform” on their homeworld Zerus. The Xel’Naga are responsible for manipulating the evolution of the Zerg, allowing the larval Zerg to parasitically merge with other creatures, taking control of their host’s nervous systems. From here, the Zerg can mutate the host and add its DNA to the Zerg gene pool for other Zerg larvae to mutate into. This method of assimilation means that there is no distinctly typical Zerg, rather many different strains and breeds of Zerg, each based on the original core genus. However, the style of the Zerg is consistent, with breeds using a carapace for armor, and using spines, claws and acids for attacking enemies. Each strain serves a distinct role and possesses the traits necessary to fulfil its function. Zerg colonies also exhibit similar roles, with each structure built within a colony essentially making up an organ in a larger lifeform. Zerg colonies produce a carpet of bio-matter referred to as the “creep”, which essentially provides nourishment for Zerg structures and creatures. The Zerg are also shown to be highly dependent on their command structure: if a Zerg loses its connection to the hive mind, it becomes completely uncontrollable and attacks anything in sight.
In StarCraft, the Zerg are obsessed with the pursuit of genetic purity, and are the focus of the game’s second episode. With the Xel’Naga–empowered Protoss targeted as the ultimate lifeform, the Zerg invade the Terran colonies in the Koprulu sector to assimilate the Terrans psionic potential and give the Zerg an edge over the Protoss. Through the actions of the Sons of Korhal, the Zerg are lured to the Confederate capital Tarsonis, where they capture the psionic ghost agent Sarah Kerrigan and infest her. Returning to the Zerg base of operations on Char, the Zerg are attacked by the dark templar Zeratul, who accidentally gives the location of the Protoss homeworld Aiur over to the Zerg Overmind. With victory in sight, the Overmind launches an invasion of Aiur and manifests itself on the planet. However, at the end of the game, the Protoss high templar Tassadar sacrifices himself to destroy the Overmind, leaving the Zerg to run rampant and leaderless across the planet.
The Zerg return in Brood War initially as uncontrolled indisciminate killers. Through the early portions of Brood War, Sarah Kerrigan is at odds with the surviving cerebrates, who have formed a new Overmind to restore control of the Swarm. Through allying herself with the Protoss, Kerrigan strikes at the cerebrates, causing disruption at their plans. Eventually, the UED fleet takes control of Char and pacifies the new Overmind with drugs, putting the cerebrates and most of the Zerg under their control. Kerrigan retaliates by allying with the Dominion and the forces of Jim Raynor and Fenix, regaining the ground lost to the UED. However, she later betrays this alliance, dealing long-term damage to her allies’ infrastructures. Proceeding to blackmail Zeratul into killing the new Overmind, Kerrigan’s forces destroy the remnants of the UED fleet, giving her full control of the Zerg and establishing the Swarm as the most powerful organization in the sector.