Brainsuckers are tick-like in appearance, with a large proboscis that it uses when it attacks. Brainsuckers have a charming standard attack pattern. When they spot a target, they leap at its head much like a Headcrab. When it latches on, it bites with its proboscis to deliver Micronoid Aggregate, microscale organisms with incredible telekinetic powers that are found in all aliens. When it is done, the host is under permanent alien control, and the Brainsucker dies.
Brainsuckers have very few life support functions and virtually no organs besides a well-developed heart and cardiovascular system. Brainsuckers hatch from eggs that can be fired from Brainsucker Launchers.