Zergling

Overview

Zerglings are the grunts of the Zerg Swarm from the StarCraft games. Their DNA came from a creature called the Dune Runner native to Zz'gashi until the Overmind integrated them into the Swarm. Their physiology may have been altered to allow them to have certain mutations and improved combat and agility skills. The genetic essence used for constructing Zerglings comes from a Spawning Pool and like all other Zerg hey are hatched from Larva at Hatcheries. They resemble somewhat of a cross between a velociraptor and a locust and are covered in a spiny exoskeleton but is rather thin compared to other Zerg units. They move around by sprinting on a set of powerful hind legs and forelegs (the former of which are webbed to indicate they might have some ability to swim, though they are granted no such feature in the game, and the latter of which are tipped with massive scythe-like claws for both attacking and burrowing underground). A third set of short limbs jut out behind its head and are used to maul its prey along with it sharp teeth and tusks. They typically move in packs with Hydralisks or other Zerglings as small ground armies or scouting parties. In-game, Zerglings can benefit from both the Melee Attack upgrade and the Carapace upgrade.
 

STARCRAFT  

ZERGLING	STATS
Race	Zerg
Type	Ground-biological
Role	Fast melee unit
Armament	Claws
Resources	25 minerals
Supply	0.5 units (2 spawn per 1 unit)
Transport slots	1
Build time	28 sec
Hit points	35
Armor	0 (add 1 per Carapace upgrade)
Attack (ground)	5 (add 1 per Melee Attack upgrade)
Cool down	8 (6 with Adrenal Glands upgrade)
Attack range	1
Sight range	5
Movement speed	Normal (Fast with Metabolic Boost upgrade)
Built at	Hatchery/Lair/Hive
Requires	Spawning Pool
Hotkey	Z

Abilities

BURROW: allows some ground units to go underground, which restores health faster and keeps the units cloaked.
Resources: 100 minerals, 100 gas 
Research time: 80 sec
Researched at: Hatchery/Lair/Hive 
Hotkey: B 
Use key: U 
 

Upgrades

METABOLIC BOOST: increases movement speed of the Zergling. 
Resources: 100 minerals, 100 gas 
Research time: 100 sec
Researched at: Spawning Pool 
Hotkey: M

ADRENAL GLANDS: increases the rate of the Zergling's attack by 20% 
Resources: 200 minerals, 200 gas 
Research time: 100 sec
Researched at: Spawning Pool 
Requires: Hive 
Hotkey: A 

STARCRAFT GHOST

The Zerglings in StarCraft Ghost is one of the enemies in the Campaign. They look a bit different from their sprite counter-part.  In their new model, their upper/back limbs are longer and don't have fingers but rather one big claw. Also their feet are no longer webbed and their tusks are noticeably bigger and jut outward more. In-game they have several abilities such as Bloodlust, which increase both damage and speed. In the Invasion mode of the game, Zerglings can transform into a Hydralisk, Mutalisk or Infested Marine. 
 
Because a final product of the game has never been released, little information has been revealed about the Zergling's role beyond gameplay footage.

STARCRAFT II

In the StarCraft II trilogy, Zerglings have gone under a major evolution much like the rest of the race. They now have wings, which appear after the Metabolic Boost upgrade, making them faster. They can also evolve into Banelings after the Baneling Morph upgrade, after which they become a new and slower but have a powerful suicide attack. 
 

ZERGLING	STATS
Race	Zerg
Type	Ground-biological
Role	Fast melee unt
Armament	Claws
Resources	25 minerals
Supply	0.5 units (2 spawn per 1 unit)
Transport slots	1
Build time	24 sec
Hit points	35
Regeneration per second	0.2734
Armor (light)	0 (add 1 per Carapace upgrade)
Attack (ground)	5 (add 1 per Melee Attack upgrade)
Cool down	0.696 sec (0.587 sec with Adrenal Glands upgrade)
Attack range	1
Sight range	8
Movement speed	2.9531 (4.6991 with Metabolic Boost upgrade) (x1.3 on creep)
Built at	Hatchery/Lair/Hive
Requires	Spawning Pool
Hotkey	Z
Evolves into	Baneling

 

Abilities

BURROW:   allows some ground units to go underground, which restores health faster and keeps the units cloaked 
Resources: 100 minerals, 100 gas 
Research time: 100 sec
Researched at: Lair/Hive 
Activation time: 2 sec to burrow, 1 sec to unburrow
Hotkey: B 
Use key: R 

BANELING MORPH: transforms the Zergling into a Baneling 
Resources: 50 minerals, 50 gas 
Research time: 20 sec
Research at: Baneling Nest
Requires: Baneling Nest 
Use key: E

Upgrades

METABOLIC BOOST: increases movement speed of the Zergling. 
Resources: 100 minerals, 100 gas 
Research time: 110 sec
Researched at: Spawning Pool
Hotkey: M

ADRENAL GLANDS: increases the rate of the Zergling's attack by 20% 
Resources: 200 minerals, 200 gas 
Research time: 130 sec
Researched at: Spawning Pool 
Requires: Hive 
Hotkey: A 

Strategies

Since Zerglings physical movement speed and attack speed are so fast, when they travel in groups they fair well against ranged units with a slow movement and attack speed because the enemy wastes too much time focusing their fire at a single target (Dragoons, Stalkers, Marauders) . 
 
Because Zerglings are so small and take so little resources they are spawned in pairs nearly doubling their output over many other units. It's for this reason that players will commonly produce them en-masse at the beginning of the game and send them to attack the other player(s) early on before they have any real defenses. This strategy became notoriously as the "Zerg Rush". 
 
Zerglings can burrow to regain health after being attacked and drop off radar from non-cloak-detecting units or use it to ambush armies, thus bypassing ranged suppression fire and going right into the fray.

Zerglings cannot fend against flying units and are in general weak against well armored units with a fast range attack or units that attack using splash damage (Firebats, Reavers, Helions, Archons, Banelings).