Brain Worm

Brain Worms were a species of parasitic worms from the desert planet of Geonosis. They are known for being able to infect sentient beings within the galaxy, including Humans, and could even infect dead corps to create an army of undead zombie-like creatures.

Usage by Queen Karina
During the Clone Wars, the Geonosian Queen, Karina the Great, used several Brain Worms to control an army of undead Geonosian Warriors by using the worms to control the dead, decaying bodies, as a means of protecting herself from military forces from the Galactic Republic during the first battle of the Clone Wars, which took place on Geonosis.

Second Battle of Geonosis
A year later, when the Separatist Alliance took back control of Geonosis and forced the Republic to launch another invasion against the natives. During this invasion, after the Separatists were defeated by the Republic, Karina tried using her Brain Worms to infect a Mirialan Jedi Master, Luminara Unduli, but this plan failed, ending with both the death of Karina, and her Brain Worm-infected 'zombie' army. Despite this, a few of Karina's Brain Worms survived, one of which managed to infect a Republic Clone Trooper. This infected clone would then collect Brain Worm eggs and brought them aboard a Republic Medical Frigate that his squad was stationed on, resulting in a massive outbreak of Brain Worms aboard the ship, which would quickly be stopped by Togruta Jedi padawan, Ahsoka Tano, who, with the aid of her human Jedi Master, Anakin Skywalker, discovered that the Brain Worms had one weakness, if they were exposed to extream cold, they would be forced to leave their host and die.