Feral zerg

Feral zerg are zerg not under the control of any higher entity. These zerg will simply attack everything around them, acting on the lowest level, and acting as predators, consuming other animals for nourishment. Control can be re-asserted over feral zerg by command strains however, even those as low as overlords.

History
During the Great War, the zerg in Zasz's Garm Brood went feral after the Zeratul slew Zasz on Char. These renegade zerg posed such a threat to the Swarm that Daggoth ordered the entire brood eradicated.

In the immediate aftermath of Overmind's destruction, nearly all the zerg on Aiur became feral and went on a rampage killing everything in their path. Even after Sarah Kerrigan took control of the Swarm, the zerg on Aiur remained outside her direct control. When Zeratul returned to Aiur in 2504 to visit the Overmind's final resting place, he found many feral zerg guarding and feeding off its corpse. Likewise, the zerg on the planet Cavir remained feral after the death of their master Daggoth following the end of the Brood War.

In the aftermath of Kerrigan's de-infestation during the Second Great War, the Swarm splintered into multiple factions, and many zerg turned feral. The zerg on Char that had previously been guarding Kerrigan immediately turned feral and began devouring everything in sight, including the corpses of zerg killed by Raynor and his men during their escape.

Feral zerg on Astrid III developed the Swarmling-strain of the zergling. This adaption caught the attention of Kerrigan, who seized control of the ferals and used them to destroy the local Dominion garrison.

On Kaldir, the zerg in Nafash's brood became feral after the protoss killed Nafash. When Kerrigan arrived on the planet, she quickly re-inducted these ferals into the Swarm.

Feral Impaler colonies resided on Marek V. On Kerrigan's orders, hydralisks from the Ryloth Brood killed and harvested the colonies' essence to evolve the Impaler-strain.

Kerrigan later telepathically seized control of a group of surviving Lurkers on Cavir, a former and used them to fend off the feral zerg threatening a Lurker den she desired.

Feral Brood lords and Mutalisks could be found near the Dominion defense platform Sigma Centari. Kerrigan had her zerg kill these ferals in order to collect their essence and reacquire the brood lord strain for the Swarm.

During the End War, many feral zerg, particularly those on Aiur, fell under the control of Amon, who used them to create his own zerg brood.