Harvesters are beings that apparently have a vital role in harvesting the protein from captives to feed The Sphere. They come in two varieties, one which walks around on mechanical legs (which can be blown off) and can travel freely through a network of organic tunnels, and another which has attached an anti-gravity device to itself, allowing it to fly freely through the air. When killed, these flying Harvesters will explode, potentially damaging the player. Both kinds of Harvesters are armed with Crawler Launchers, but only the walking variety uses the alternate fire, creating a shield to protect themselves whenever the player uses explosive weapons. If the player manages to destroy its mechanical legs, he must be quick to dispatch the crawling torso before it reaches a tunnel, where it can provide itself with another set of mechanical legs.
Harvesters are reptilian-like looking creatures with a visor covering their eyes. They have quadruped mechanical legs and mandibles.
- The flying Harvester version has been said to bear a resemblance to the Assault Commanders from Duke Nukem 3D.