A species of parasitic worms originating from the planet Geonosis, known as brain worms, possessed the capability to infiltrate a host's body, seize control, and potentially dominate entire societies. During the Clone Wars, a conflict between the Galactic Republic and the Confederacy of Independent Systems, the Geonosian Queen, Karina the Great, employed these brain worms to command a legion of undead Geonosians.
Following the defeat of Karina and [her](/article/gender] underlings by Republic forces, a brain worm successfully infected clone trooper Scythe. Scythe, now under the worm's control, proceeded to spread the infection among numerous other clones within Tango Company, as well as the Jedi Padawan Barriss Offee, all aboard the Republic medical frigate TB-73. Ahsoka Tano, another Jedi Padawan, intervened to prevent further spread of the infection by utilizing extremely low temperatures to neutralize the worms, thereby rescuing Offee and the majority of the troopers.
The brain worms exhibited a tendency to manipulate their hosts' minds by tapping into the biologically stored memories of the Geonosian queens, even after the physical death of the host. In the course of the Clone Wars, Queen Karina the Great orchestrated an army of undead Geonosian warriors to realize her ambitions following the successful capture of their planet by Republic forces.
These worms also demonstrated the capacity to seize control of the minds of living individuals, including clone troopers and even Jedi. While dominating the minds of clone troopers, the worms could convincingly mimic their hosts to avoid detection. They could even access memories relevant to their objectives, notably the knowledge of how to best incapacitate Jedi, which allowed them to claim Barriss Offee's body for their collective consciousness.
Remarkably, a solitary brain worm could completely usurp the mind of a Jedi, dictating her physical actions, accessing her memories, utilizing her lightsaber skills, and harnessing her Force abilities. The worm's initial demonstration of Offee's Force powers evoked a smile on its host's face as it employed them to attack Tano.
Queen Karina the Great leveraged the worms to command a force comprised of undead Geonosian soldiers. After the defeat of all surface combatants during the Second Battle of Geonosis and the destruction of the droid factory, Luminara Unduli discovered her deep within the Progate Temple. Anakin Skywalker and Obi-Wan Kenobi tracked Unduli after communications were lost, and the queen desired to possess all three Jedi with her brain worms until Kenobi's 212th Battalion destroyed the temple, allowing the Jedi to escape with Poggle while the queen was buried alive.
Following Karina's presumed fatal entombment, clone trooper Scythe became infected by a newly hatched brain worm, which subsequently spread the worms among the clones in his company during an ad hoc medical resupply mission from Ord Cestus to Dantooine. After attacking the two Jedi Padawans assigned to the relief mission, Ahsoka Tano and Barriss Offee, the clones succeeded in isolating and infecting Offee, whose memories revealed Tano's location as the only uninfected person remaining aboard the vessel. The two Padawans engaged in combat, with Tano on the defensive only, until her master discovered that the worms were extremely vulnerable to cold temperatures by torturing Poggle with the use of dark side Force abilities.
Armed with the knowledge that low temperatures could expel the worms from their new hosts, Tano breached the frigate's coolant system. The ensuing freezing conditions rapidly immobilized the clones, although the worm possessing Offee exhibited resistance to the cold due to its host's natural resilience to freezing temperatures. Pursuing Tano throughout the ship, the pair clashed once more on the bridge as the vessel approached the medical station at a perilous speed. During the duel, Tano managed to direct a burst of coolant at Offee, briefly freeing her from the worm's control long enough for her to plead for Tano to kill her for the greater good. Tano, however, ensured her friend's survival by targeting the worm, which desperately protruded from Offee's mouth in a futile attempt to withstand the lethal conditions.
With the frigate safely docked, a quarantined expedition led by Kit Fisto boarded the vessel and discovered the severed halves of a brain worm at the feet of an unconscious Offee, cradled in the arms of a delirious Tano who was determined to complete her mission by loading the ship with medical supplies before losing consciousness herself.
Upon awakening, Tano was immediately greeted by her master at her bedside, who promptly reassured her that her efforts to stop the worms had saved her friend Offee as well as most of the clones. Tano then presented to her master the moral dilemma she faced aboard the frigate: whether or not to eliminate her possessed friend for the greater good. Her master informs her that being a Jedi means ensuring the safety of every life in their care, and assured his Padawan of Barriss' inevitable gratitude once she awakens.