Larva

The Larva is the base Zerg unit from which all other units and, ultimately, buildings are created.

Overview
Larva are the closest creatures to the original Zerg insectoids. Although their size and toughness were greatly boosted by the Xel'Naga during their experiments, they still possess the two traits that originally intrigued the ancient masters: genetic versatility and psychic sensitivity.

Maggot-like, Zerg Larvae contain within them the genetic code for all other Zerg breeds. When a new breed of Zerg is needed, an individual Larva will enter a pupal state and begin replicating the DNA of one specific Zerg breed at an astounding rate. After a short gestation period, the new mature Zerg hatches.

A young hive will only have the genetic code for the most basic of Zerg breeds, such as the Drone, but as it grows and develops new structures, its library of genetic strains is expanded. With a command from the Overmind, the Larva will enter a pupal state and begin the metamorphosis into whichever breed is required by the hive.

It is worth noting that Larva has the dubious 'honor' of being the first Zerg strain ever encountered by the Terrans of the Koprulu Sector. In the late 25th century Larvae were discovered on a number of Fringe Worlds. These worlds were depopulated by "cholera" and the specimens shipped to a Confederate science facility on Vyctor 5, only to be discovered by the Sons of Korhal years later.

StarCraft
Larvae are automatically produced by a Hatchery, Lair, or Hive over time, up to a maximum of three at any one time per building. Players may only order Larvae to evolve into other units. Larvae automatically 'wander' near the building that spawned it. If the Creep under the Larva dissipates, the Larva will die instantly. Canceling an evolution will also kill the larva.

StarCraft: Ghost
Concept art for Larva appears for StarCraft: Ghost. As seen, the Larva appears larger and more adept at battle.

StarCraft II
Larvae are produced every 20 seconds from a Hatchery.

Abilities

 * Mutate:
 * A larva can produce a large variety of units: Drone, Overlord, Zergling, Roach, Hydralisk, Nydus Worm, Infestor, Mutalisk, Corruptor, and Ultralisk.