

When it is idle and no threat is visible, it will gently sway its tentacles around and emit soft hissing and groaning noises. 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. 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.

This causes it to summon reinforcements by opening its abdominal cavity to reveal a portal orb that a Shock Trooper will teleport through. 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. The Gene Worm attacks with its tentacles and also ejects a deadly chemical stream from his mouth. 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. Physically, the Alien resembles a green, worm-like being with many tentacles. 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. 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. The Gene Worm is the final boss of Half-Life: Opposing Force, and the most mysterious of the Race X aliens.
