The Brain Bugs are the smartest of the alien bug species. Though it isn't as powerful on the battle field and has to remain underground, the Brain Bug's telekinetic powers make it even more deadly. Inside the center of the Brain Bug's face is a giant hook like arm that it inserts into a human's skull and through the hook can not only suck a human brain out and eat it, but it can get into the human's mind telepathically and read the human's mind and control it to do certain functions such as making it's prey tell other humans army's by radio to head to a false location and trap the humans to be killed by the bug army.
Seeing that the Brain Bug is not fast, it requires a horde of smaller bugs to carry it through cave tunnels to get to where it wants to go.
In the animated series Roughnecks Starship Troopers Chronicles it is shown that there is more then one Brain Bug.