The roach is a particularly tough, armored breed which possesses a high-speed regeneration ability when burrowed. This quick regeneration is due to the constant breakdown to the roachs's own modified pharynx, a natural byproduct of the zerg's acid production, an intentional design by the Swarm in order to facilitate quicker regrowth. A roach is slightly shorter than a terran wearing CMC armor. In order to properly form, roaches require dark, humid conditions, such as those found in a roach warren.
Roaches evolved from the fast-healing zantar slug of Garrxax and were in use by 2501, taking part in a battle on Shi. Their ranged acid saliva attack is capable of penetrating neosteel and armor, and violently dissolving flesh on multiple entry points. This saliva is derived from the zantar slug and is expelled with considerable force through the muscles that surround the roach's salivary glands—highly specialized striated ducts that produce a unique enzyme that weaponizes the creature's already corrosive saliva. This acid contains viroids that propagate through their victim's nervous system, which can only be either addressed through heavy bachteriophage treatments or by removal of the affected limb. Due to their heavy armor, roaches are unable to aim their acid at aerial targets.
If pressed into close quarters, roaches use scythe-like blades on their backs to dispatch the enemy. The hardness of these scythes allows roaches to scythe through neosteel and armor with ease. Roaches have the ability to evolve into ravagers, a fierce artillery strain that lobs corrosive bile at a long range.
The roach's metabolism is ten times greater than that of the zantar slug (increased through assimilation), and gained the ability to quickly regenerate even the most grievous wounds when burrowed. This is through a process known as osmotic epithelium. The absorption of soil compounds, especially rare earths and metals, has allowed roaches to develop extremely thick carapaces. Some Dominionscientists have theorized that the roach is not immune to the ravages of its acidic body fluids, and the creature's potent regeneration capabilities ensure tissue integrity in spite of constant corrosion. The roach's thoracic acid bladder is similar to those organelles found in mutalisks. This bladder is triggered to erupt when penetrated.
Roaches enslaved by the Cerberus Program had their carapaces enhanced with a carbon fiber nanoweave, and their offensive capabilities improved with forged titanium blades. 
After the ascension of Zagara to supreme ruler of the swarm, Abathur was ordered to continue to experiment with the roach genome in a continuing pursuit of perfection. This resulted in variant strains of the roach.
"Use heaviest weapons only and confirm kill shot. I repeat, be 100 percent sure of total kill! Those bastards heal real fast, so do not settle for injury! If they burrow, grenade them as they go down!"
One on one, few are capable of taking on a roach and winning. They are deployed when zerglings start to be thinned out and are sometimes supported by infestors. When paired with zerglings, they can be nearly unstoppable against marines bereft of siege tank or bunker support. Roaches are nearly impervious to small-arms fire, and nigh immune to flame-based weapons, and explosives and artillery are a must for terran forces when these creatures are deployed.
The roach is a ranged unit, giving it added utility at choke points. The roach rises slightly when it attacks. It also has a melee attack that it, like the hydralisk, performs at close range for the same damage as the ranged attack.
They have no anti-air attack. Roaches inherit the roles of medium attacker and ambusher from the original StarCraft's hydralisk and lurker. To compensate for its lack of anti-air attack, it is common to see roaches combined with hydralisks. A common strategy is for roaches to absorb damage while hydralisks deal it.
Roaches can morph into ravagers in Legacy of the Void.
Upgrades and Abilities
Increases Roach movement speed to 4.2 while unburrowed, and to 4.4 while burrowed under creep.
Base composition of roach acidic saliva identical to that of zantar slug. Highly corrosive. Can alter chemical compound. Systematically evolve bile duct membranes, force production of hydroiodic bile. Upon contact, will melt tissue, flesh, bone. Dissolve poorly armored foes.
Roach can move at full speed while burrowed. Doubles roach regeneration rate while burrowed.
Can enhance roach utility, several key evolutions. Able to evolve tunneling claws, series of spiracles lining carapace. Will allow roach to tear through terrain while burrowed, draw additional nutrients from soil. Combination provides strategic advantage.
Zagara is able to summon sacs of roaches with timed life in Co-op Missions. Otherwise, roaches are exclusive to Abathur. Abathur is able to evolve his roaches into ravagers, and they upgrade to the vile strain when he reaches Level 14. Additional upgrades for roaches and ravagers are unlocked when Abathur reaches Level 4.
Roaches gain +3% hit points, +1% attack speed and +5% armor per stack of Biomass. Can stack up to 100 Biomass. Passive: Heal 1% hit points per Biomass.
Essence Hoarder: Roaches can collect an additional 25 Biomass (summary 125).
The Limitless: Roaches can collect an additional 100 Biomass (summary 200), but gain +1.5% hit points, +0.5% attack speed and +2.5% armor per stack.
The amount of collected biomass change based on difficulty and the amount of supply used by the killed enemy unit:
Collect 5 biomass per supply (Casual and Normal)
Collect 4 biomass per supply (Hard)
Collect 2.5 biomass per supply (Brutal)
Hit Points: +4.35 per Biomass. Up to a maximum 580 Attack Speed: +1% per Biomass. Up to a maximum 1 Armor: +0.05 per Biomass. Up to a maximum 6>>7>>8>>9
With Essence Hoarder
Hit Points: +4.35 per Biomass. Up to a maximum 688.75 Attack Speed: +1% per Biomass. Up to a maximum 0.89 Armor: +0.05 per Biomass. Up to a maximum 6.25>>7.25>>8.25>>9.25
With The Limitless
Hit Points: +2.175 per Biomass. Up to a maximum 580 Attack Speed: +0.5% per Biomass. Up to a maximum 1 Armor: +0.025 per Biomass. Up to a maximum 6>>7>>8>>9
On normal and rush maps, roaches are well suited for the early and mid-game.
Zerg vs Terran
A roach/baneling combo is very powerful against terrans, as the roaches will soak damage, enabling the banelings to get close to the enemy and deal their high damage attacks.
Zerg vs Zerg
Roaches and zerglings are used early in ZvZ matches. Roaches are a more defensive unit compared to zerglings. Cost for cost, roaches win against zerglings at chokepoints but lose in open areas. Later in the game, numerous roaches can defeat numerous zerglings even in open areas.
Zerg vs Protoss
Roaches are a great way to defend an early expo against 2 Gate zealot push. Mass overwhelming roaches is also quite strong against a fast teching opponent, even one who goes air. Use roaches to soak up colossus damage until ultralisks or air units can support.
Roaches, coupled with their speed and burrow move upgrades, make great harassment units at exposed bases.
Roaches are a great staple unit and have great value for cost, but take up control quickly. In direct encounters with enemy armies of equal supply, mass roach is more likely to lose.