Zerglings form the most numerous of the zerg mutations - their simple DNA allows two zerglings to be spawned from a single larva. The larvae get the genetic information from the 'primordial ooze' of spawning pools. Zergling replication is so efficient that they thrive even when exposed to exceedingly high mortality rates.
Zerglings are the smallest zerg strain apart from the larvae, and equivalent in size to a large dog, zerglings are one meter tall and possess webbed feet. Further mutations may be made to zergling DNA, namely the alteration of their physiology through a metabolic boost to increase their reflexes and rate of movement and the mutation of their adrenal glands, changing their glandular balance to induce a battle frenzy. These adrenal glands have been observed to be unusually large for a creature of the zergling's size. Further analysis has revealed evidence of genetic manipulation, which also increased zergling aggression, driving them into a state of frenzy. In such a state, zerglings can bring down armored vehicles and structures with ease.
The rapid genesis modification to zergling cells allows their gestation to proceed at remarkable speed. Zerglings have tough, adaptable, leathery skin which prevents moisture loss, while still allowing fluid circulation to keep the zergling's body temperature at appropriate levels. As per their origins, zerglings have an efficient nutrient storage system. Zerglings can derive the necessary compounds for life from anything they eat. This allows zerglings to operate away from a hive cluster for extended periods of time.
Zerglings are physically adaptable creatures, able to climb near vertical surfaces and are extraordinarily fast, though they are generally easy to exterminate, one ending up as roadkill after being run over by a recon vehicle. Zerglings have a complex optical structure, and their eyes have an optical aperture which allows them to see in the dark. This ability is further enhanced by a layer of tissue that reflects light, and the production of a substance which, depending on saturation levels, makes a zergling's eyes glow orange or red. This glow is an indicator that a zergling's vision has fully adapted to whatever low-light conditions it has found itself in. However, zergling eyes have also appeared as pure black in such conditions.
The zergling's spiked tail allows the creature to maintain balance while running at high speeds. The spikes that extend from the tip have no discernable purpose, and Dominion scientists have speculated that it is vestigal from their dune runner forebears.
Outside of combat, zerglings can serve as lookouts and lone zerglings serve as scouts, though may have a retinue of hydralisks if they scout an exceedingly long distance away from a hive cluster. When they attack however, zerglings move in large groups, ranging from a dozen to a hundred, often acting as "meat shields" for more powerful zerg strains. Individually, zerglings are little more than feral animals, but work well in large groups under the command of larger zerg warriors. In combat, zerglings are fond of ripping enemies to shreds with their sickles and fangs, indicating a sadistic streak. When paired with roaches, they can be nearly unstoppable against marines bereft of siege tank or bunker support. Zerglings are allergic to lemon juice. During the Second Great War, its validity became a Terran Dominion rumor. Abathur resolved to solve the problem. [Source: wikia]