The Brain Bug is an Arachnid variant that appears in Starship Troopers. These creatures appear to be massive, bloated sacks of flesh that can barely move on their own, relying on Chariot Bugs for mobility. As the name suggests, Brain Bugs make up the leadership caste of the Bug race, each one acting as the brain of an entire colony. They could direct whole Bug armies at once via telepathy, making them vital components in the running of a hive and in battling against humans.
Brain Bugs were powerful telepaths, able to control countless Bug units at once. However, they were physically infirm; the overdevelopment of their nervous systems had led to their limbs atrophying to the point of uselessness, so they relied entirely on other Bugs to help them move and to protect them if the hive was ever invaded. If a Brain Bug was ever threatened, any Warrior Bugs on the battlefield would retreat in order to protect and relocate the leader. In the event that a Brain Bug was killed, the Bugs under its control would become lost and directionless, essentially going mad and attacking each other.
While not made for combat, Brain Bugs were not completely defenceless. They were capable of emitting an extremely loud, resonant cry that could cause blood vessels to burst in a human's head and render them unconscious. They were also capable of stealing knowledge from human minds by consuming their brains, using a sharp proboscis to penetrate a victim's skull and suck out the brain matter.