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I guess you're a good guy corporal. Listen, you've got to get down below, there's something coming through and it's the nastiest-looking thing yet. Some of your buddies went down there a while ago and I haven't seen them since. I've got some weapons pilled up in here, you better take as much as you can carry. Because I think this is it. Good luck corporal.
~ A Security Guard to Corporal Shephard.

The Gene Worm is the main antagonist of the 1999 video game Half-Life: Opposing Force created by Gearbox.


The Gene Worm is the final boss of Half-Life: Opposing Force, and the most mysterious of the Race X aliens. This life form is said to be the equivalent of a "biological resource management factory." It is suspected to be capable of taking any of Earth's natural resources and assimilating it to make them useful to the aliens' needs. If one fully entered Earth and became productive, he would effectively alter the planet enough to become useful as a new homeworld for Race X. However, this was never shown in action.

Physically, the Alien resembles a green, worm-like being with many tentacles. It bears a striking resemblance to the Xen Tentacle, appearing to have green skin with many tentacles and possessing a beak-like protrusion similar in both shape and position.

The Gene Worm attacks with its tentacles and also ejects a deadly chemical stream from his mouth. Its outer hide is impervious to damage; in order to kill it, the player must blind him by shooting both eyes with the mounted laser guns on either side of the worm. This causes it to summon reinforcements by opening its abdominal cavity to reveal a portal orb that a Shock Trooper will teleport through. The worm's weakness is by firing any gun at the rear of this stomach cavity; It should be noted that the portal orb itself is not vulnerable. When the Gene Worm "dies", it sinks back into his portal, but not before emitting a "portal storm" into the room, similar to the one that occurred as the Nihilanth died. When it is idle and no threat is visible, it will gently sway its tentacles around and emit soft hissing and groaning noises.

The Gene Worm is found deep underground in a seemingly abandoned industrial area of Black Mesa and appears through a portal opening powered by Sprites in a room there, apparently either unwilling or unable to fully enter this world, most likely because of the minuscule size of the portal behind it in proportion to the Gene Worm's presumably immense size and length. The room itself has been fitted with mounted weapons which are powered by Xen energy crystals. The player character, Adrian Shephard, is sent down to the portal by a Black Mesa security guard, who remarks "Some of your buddies went down earlier, and I haven't seen 'em since." These soldiers were only able to set up the mounted weapons before their unseen demise, although nothing is seen of their remains, possibly indicating they may have been "processed" by the Gene Worm itself.



  • The Destroyer, an enemy featured in the Gearbox game Borderlands is remarkably similar to the Gene Worm, in the sense that it has many tentacles, has an eye which needs to be shot in order to kill it and the fact that it appears through a portal. The Destroyer is not, however, an intentional reference to Opposing Force.
  • The Gene Worm somewhat resembles the fictional Shoggoths from the works of author H.P. Lovecraft himself.
  • In the Opposing Force files, there is a sound byte related to the Gene Worm called "dsbossit". When played, it sounds like plain gibberish. But when played backwards, it seems to say "To win the game you must kill me, Randy Pitchford". Randy Pitchford is CEO of Gearbox. This is a nod to Doom 2 where "to win the game you must kill me, John Romero" is played backwards when the final boss sees the player. Furthermore, dsbossit is the name of this sound in Doom 2's main WAD file.
  • There is a glitch where on some Linux and Mac systems, the gene worm will retreat too quickly upon defeat. After this, the portal storm will still happen but when the big portal appears, the player will not be teleported and will be unable to complete the game.


           Halflifenavbox.png/ Portalnavbox.png Villains

Half-Life: Nihilanth | Zombies | Hazardous Environment Combat Unit | G-Man | Employers

Half-Life: Opposing Force: Gene Worm | Race X | Black Operatives | United States Government | G-Man | Employers

Half-Life 2: Wallace Breen | The Combine | Combine Advisors | Overwatch Elite | Combine Overwatch | Civil Protection | Stalkers | Zombies

Half-Life 2: Episode Two: Combine Advisors | Barn Advisor | The Combine | Zombies

Half-Life: Alyx: G-Man | Combine Overwatch | Zombies | Jeff | Scientist | Combine Advisors | Employers

Portal: GLaDOS | Turrets | Aperture Science

Portal 2: Wheatley | Cave Johnson

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