The Control Bug is a parasitic mind-control weapon used by the Bug Horde.
A parasite bug is produced inside a human host. Several can be spawned at a time. The larva is vomited by the host and searches for an uninfected human immediately after birth, whereupon it will then proceed to crawl down their throat.
The parasite bonds to the host's spinal column, replacing the central nervous system. It then begins absorbing nutrients from the host, who begins to rot from the fingers up, which is often mistaken for muzzle burn. The spy bug can quietly subvert the host to the Bugs, or attack any other uninfected individuals nearby directly. If the Parasite chooses the second option, the host begins decomposing in earnest, starting to resemble a corpse within hours.
The Spy bug more or less completely consumes and replaces the hosts brain. It then cuts open the skull of the host, who is little more than a talking corpse at this stage. Another host then drags them to a populated area, and tears off the top of their head before extracting the mature spy bug. The spy bug's posterior is covered in parasite bugs, which split off and swarm the opposition when the mature spy is killed.