Essence

Essence was the genetic information carried by all life and the key to zerg evolution. By consuming or assimilating their prey, the zerg took its essence and incorporated the desired strengths of that creature into themselves, a unique ability that motivated the fallen xel'naga Amon to enslave the zerg during their uplifting on Zerus. The zerg were said to possess a purity of essence, a quality shared with certain other species, and the manipulation of essence underlay nearly every adaptation the Swarm ever made.

Origin and storage#

According to Zurvan, the Ancient One, the first zerg were born when a single essence split into many. Within the first spawning pool on Zerus these essences fought and devoured one another and grew stronger, eventually giving rise to the zerg as a species. On Zerus itself essence could be found in some bodies of water. The ability to steal essence and absorb a prey creature's strengths was what first drew the fallen xel'naga Amon to the zerg, who enslaved them during their uplifting and set in motion the creation of the Overmind.

Within the Swarm, the essence of each zerg type was stored in specific hive structures, such as the lurker den, which allowed hive clusters to spawn their various minions from larvae. This dependence on stored essence became a vulnerability after Sarah Kerrigan's deinfestation, when the fragmenting of the Swarm during the Second Great War cost the zerg the essences of many strains. They were forced to seek the lost strains among feral zerg and to reassimilate their essences through capture or consumption. The corruptor's essence was lost completely and remained unrecoverable for the rest of the Second Great War.

Uses and properties#

The amount of essence required for a successful evolution varied with the strain. To evolve the creeper strain of the swarm host, only a single ash worm needed to be killed, whereas evolving the impaler strain of the hydralisk required the destruction of multiple impaler colonies before enough essence had been collected. In other cases essence from specific individuals of a chosen species, such as an ursadon matriarch, had to be gathered to augment the Swarm appropriately.

New essence could also be acquired without assimilating another species. During the zerg invasion of Korhal, Abathur used the side effects of the Terran Dominion's experimental weaponry to evolve two new strains of ultralisk, and new strains could be developed through repeated cycles of natural selection, as with the vile roach and the hunter baneling. Beyond producing new strains, the Swarm could use its hive mind to rapidly manipulate the essence of any existing zerg on a wide scale at any moment, letting it adapt to changing conditions such as the flash freezes of Kaldir. Where enough essence was available, deceased zerg could even be revived or reconstituted, and powerful primal zerg such as the primal Queen of Blades and Dehaka could twist essence to heal themselves and nearby allies.

Limits and difficulties#

Not every essence could be taken into the Swarm. The protoss could not be assimilated, the Khala and the energies of the Void protecting the Khalai and the Nerazim respectively, and protoss genetic material itself could not be used by the zerg. Hybrid essence, though strong, could likewise not be consumed. After the End War, Overqueen Zagara, in keeping with Kerrigan's wishes, forbade the Swarm from assimilating the xel'naga essence recovered from Ulnar and instead created creatures outside Swarm control to house it.

Some essences proved difficult even after they had been assimilated. Abathur noted that the swarm host's primal essence constantly adapted and rejected even simple mutations, and different essences could compete with one another, as the raptor and the swarmling did, making it impossible to combine them in a single strain. Psionic essence always posed a particular challenge. The overlord's essence remained virtually identical to that of the original Gargantis proximae, and Dr. Talen Ayers theorized that the zerg had deliberately left the Gargantis genetic code largely unchanged to preserve its psionic abilities. Despite the Swarm having first targeted humanity for its psionic potential, Abathur considered terran essence unimpressive; while some terrans retained their psionic gifts and intelligence after infestation, they were the exception.

Energy-based essence#

The most potent forms of essence took on a visible energy character. The essences of the primal pack leaders on Zerus appeared as purple-white energy, and after being reborn as the primal Queen of Blades on Zerus, Kerrigan slew those pack leaders and absorbed their essences. Xel'naga essence appeared as golden energy. To the xel'naga, essence, matter, information, and consciousness were interchangeable and could be converted through relics such as the Keystone. In accordance with the Infinite Cycle, an elder xel'naga would sacrifice itself to transfer its essence to a chosen offspring, transforming the recipient into a xel'naga in turn; during the final stages of the End War, Ouros imparted the last of his essence to Kerrigan, transforming her into a xel'naga and giving her the power to destroy Amon. After the End War, xel'naga essence was scarce, and what remained was used to create the adostra and the chitha, creatures whose biology exhibited patterns of the Cuccodujo series where the essence had touched them.