Approximately 0.5 meters
- "Watch as my child enters your Jedi friend."
- ―Karina the Great
Brain worms were worm-like parasites from Geonosis that had the capability of controlling minds. They hatched from yellow eggs, and were known to be used by the Geonosian Queen Karina the Great during the Clone Wars on her Geonosian minions. The worms would sometimes enter the host via the nose, and were able to control dead Geonosians.
Brain worms reacted negatively to cold temperatures.
During the Second Battle of Geonosis, Queen Karina the Great used the worms within her dead minions in the Progate Temple to endlessly pursue the search party sent by the Republic to find Jedi Master Luminara Unduli. The search party was led by Anakin Skywalker and Obi-Wan Kenobi. Queen Karina intended to use them to control the Jedi, but didn't succeed in inserting them.
After the battle, a surviving worm hatched and crawled into one of the clone troopers of the Tango Company resting outside the Progate Temple. As the company headed to the medical frigate TB-73 going to the Ord Cestus medical station, the infected clone brought more eggs in his backpack and eventually infected the entire clone crew. The clones took control of the ship, attacking its other members, and proceeded to infect Barriss Offee. Ahsoka Tano ruptured the ship's coolant system, weakening the worms. Subsequently, Ahsoka and the infected Barriss dueled, but the cold finally got to the worm in Barriss, and Ahsoka killed it as it was crawling out. Barriss and all clone troopers aboard the ship besides Trap, the pilots, and two other clones were saved. Trap and the other two clones were killed by Barriss and Ahsoka in self-defense, and the pilots were killed by infected clone troopers Ox and Edge.
- Star Wars: The Clone Wars – "Legacy of Terror" (First appearance)
- Star Wars: The Clone Wars – "Brain Invaders"
- (First identified as Brain worm)
- Star Wars: The Ultimate Visual Guide: Updated and Expanded
- "100 and Counting"—Star Wars Insider 139