Zerg

The Zerg are the second creation of the Xel'Naga, after the Protoss. They were greatly inspired by the Tyranid race of the Warhammer 40,000 universe.

History
The planet Zerus housed a small, worm-like creature, which was perfect, as the Xel'Naga were looking to give the lowest life-form "Purity of Essence", and finding the Zerg was, to them, a godsend. They changed the Zerg from an earthworm-like creature into a parasitic "worm", which supercharged the hosts' evolution. Wishing to avoid an earlier failure (specifically, the Protoss), they imposed a hive mind on their new creation. This "Overmind" soon turned against them, and almost completely eradicated or consumed them. With the consumption of Xel'Naga, the Zerg were able to learn of the Protoss, and decided to assimilate them, to become truly perfect. However, they needed a weapon. They settled on the Terrans, who were evolving into a close second to the Protoss.

The Zerg possess the ability to terraform any planet or space platform they land on through a thick mat of gray fungus called "Creep", which spreads out from Hatcheries, Lairs, Hives and Creep Colonies, the latter of which can be mutated into defense strains. Each structure in a Zerg Hive Cluster acts as an organ in a huge super-organism, some of which have spread out to cover entire planets or platforms.

Larvae
The Larvae is spawned from the Hatcheries, Lairs, and Hives. Each larvae carries the genetic code for every Zerg strain. At first, the larvae can only mutate into Drones and Overlords, although each new organic building adds more genetic information to their repertoire thanks to the hive mind and super-organism structuring of a Zerg Hive Cluster.

Egg
"Egg" is a misnomer: it is in fact a pupae. Larvae will enter this stage once they have received a command to mutate into one of the many strains of Zerg.

Adulthood
The mutated Larvae is now combat ready. Certain strains are for melee, ranged combat, or air support while others are solely meant to produce horrible poisons. Only the Hatchery/Lair/Hive and Queen carry out any reproduction. Very few Zerg have ever lived out their natural lifespans, as they are either killed in battle, or potentially even immortal. The few exceptions are simply meant as distractions. If it is a ground based creature, it can burrow in to the ground.

Varieties
There are Numberous combative sub-species of Zerg.
 * Drone, responsible for collecting Crystal and Vespene, and construction.


 * Overlord, radiates Psychic energy to control the other Zerg with. It can be evolved into a transport class unit.


 * Zergling, evolved from small lizards, now the primary warrior strain. Spawned two at a time due to their simplistic genetic structure.


 * Hydralisk, large snake-like beast, produces spines that are hurled with enough velocity to puncture battlecruiser grade armor.
 * Lurker, mutated from the Hydralisk. It burrows and sends a row of vertical spikes into a target.(Brood war only)


 * Mutalisk, primary air combat unit. Each shot is a disease, which spreads to two other targets.
 * Guardian, a bomber creature mutated from a Mutalisk. Can only attack ground targets.(SC1 only)
 * Devourer, mutated from the Mutalisk. Can only attack air targets.(Brood war only)


 * Scourge, a small bat-like suicidal aerial unit, spawned two at a time due to their simplistic genetic structure.(SC1 only)


 * Queen (Pre Brood war), a large beast that originally resembled a sort of flying octopus, although they now move about along the ground for better protection at the cost of mobility. It is used to sow the hyper evolutionary virus, which in turn creates the Infested Terrans. Its only combat ability is spawning a pair of Broodlings on a ground unit.(SC1 only)
 * Broodling, a small, insectoid being that is fired from a Queen during its egg stage. It uses the targeted organism's DNA to fertilize it, and it is quickly born thereafter in an explosion of gore. They are unstable, however, and cannot live for very long.


 * Defiler, a rove beetle-shaped creature (specifically, a devil's coach horse beetle. It carries the gene codes of every Zerg, which it uses to produce carcinogenic (cancer-causing) poisons.(SC1 only)


 * Ultralisks, a large Triceritops like beast. The term "Living Battering Ram" is most appropriate.


 * Infested Terrans (Pre Brood War), a "zombified" suicide bomber. It produces chemicals that are not only horribly toxic, but explosive as well.(SC1 only)

Post Brood War Strains

 * Nydus Worm, a long worm-like organism that erupts from the ground and drops off other units. It is actually a tentacle of the Nydus Network. presumably uses perstalsis to move Zerg combat organisms very quickly. it also grows Creep.
 * Infester, a Zerg that resembles an armnored slug that can put other Zerg in a frenzy, Mind control other creatures, Move while burrowed, spawn Infested Terrans, and spit a gob of fungal spores at enemy warriors.
 * Infested Terran (Post brood war), the evolution of Infested Terrans. They have a poisonous attack instead of its predecessor's destructive suicide attack. However, the alteration forces them to gain a limited lifespan. A different strain extends the period to a full planetary night, however, they spontaniously combust when exposed to UV radiation.
 * Corrupter, a flying, vaguely spherical organism that can make it's victims weaker.
 * Overseer, an evolved Overlord with detection capabilities and has the power to disable buildings and spawn Changelings.
 * Roach, a ranged attacker with a supercharged regeneration ability and has the power to move while burrowed.
 * Brood lord, a Guardian like creature evolved frome the corruptor that spawns Broodlings every time it attacks.
 * Queen (Post brood war), A new version of the queen, a hive defender/overseer that can restore life, spawn extra larvae and creep tumors, pod-like organisms that produce creep. Once spawned, Creep Tumors may spawn one more Creep Tumor. This ability is passed on to it's clone.
 * Baneling, mutated from the zergling,It is a small, suicidal, Pillbug-like kamikaze creature.
 * Changeling, a shape-chnaging spy unit, named after the superstition of Faeries kidnapping children left by open windows or lost in the forest, and replacing them with a faerie child, who was close to unmanagable. it has a short lifespan.

Hive Mind
The Xel'Naga were concerned that the individuality of each Zerg would cause a war, and therefore they chose to impose a hive mind on their creation, which became known as the Overmind. Later, the Zerg were taken control of by the infested remains of the former human, Sarah Kerrigan, and the Overmind was obliterated.

Hierarchy

 * Overmind/ Infested Kerrigan
 * Cerebrate
 * Overlord
 * Minions