The following section contains information from a previous version of StarCraft II which is no longer valid.
Roaches previously attacked air units but that ability was removed from the game pre-retail release.
As of May 2008, due to a bug roaches were not affected by the Dark Swarm's secondary ability of preventing units inside it from firing. Dark Swarm was later removed from the game by October of that year.
Artistically, the physique of the roach was very similar to the lurker, leading the design team to push the lurker in a different direction so the current roach design could be retained. Originally, brown was its dominant color, but this was later changed to black.
The roach was originally a melee attacker when it was first revealed in March 2008 though it was later redesigned to be a ranged attacker, making the scything blades nearly useless aside from visual flamboyance. Its melee animation can still be seen when a roach is targeting a unit within melee range.
In April 2008 the roach regenerated at 15 HP per second (25 hp/second with Organic Carapace). A roach could heal fast enough to retain approximately 50% of its hit points if hit by a psi storm, and over 80% of its hit points after its regeneration has been upgraded. The roach's regeneration rate appears to have slowed as of April 2009.
Blizzard removed the above-ground regeneration ability, as they felt it was too "random"; roaches could win or lose battles depending on how they were randomly targeted when opposing units attack-moved against them.
In June 2010, the Organic Carapace upgrade was removed.
Greatly increases roach regeneration by +10 hit points per second.
During the Legacy of the Void beta, the roach burrow and tunneling claws upgrades were made standard. These was reverted to upgrade status. The ability to move while burrowed was temporarily removed.
The roach also gained the ability to mutate into a ravager, a specialist artillery unit.