Riftworm

The Riftworm is a major antagonist in Gears of War 2 serving as major catalysts for the game's plot. The Riftworm is a massive 8-10 mile long creature buried deep beneath the crusts of Sera and within the inner workings of the Hollow. They are semi-intelligent creatures and are known for burrowing throughout the Hollow and leaving behind waste that creates life and enriches the soil and the Riftworm is worshipped as a god by the Locust because of this. During the Siege of Jacinto, the Riftworm was deployed to burrow underneath and sink major human cities around Jacinto to pave a way for the major human stronghold to ultimately collapse itself.

Building the Hollow and Godhood
The exact origins of the Riftworm remain mysterious similiar to that of the rest of the Locust Horde, but what is known is that the Riftworm was responsible for burrowing the Hollow and paving the way for the Locusts to successfully create their capital city of Nexus and other settlements throughout the crests of Sera. The Riftworms burrowed and left behind their manure which was used to enrich the soil and even helped create life in the Hollow, leading to the giant creatures to be worshipped as gods. The Riftworm later became the central figure of the Trinity of Worms, the religion of the Locust Horde, and would also inspire both religious beleifs and architecture of the entire Locust species as a whole. It was believed that the Locust would use events such as explosions to lute Riftworms towards their intended targets and they remained underground until the Outer Hollow was attacked during the Lightmass Offensive which awoken one of the Riftworms and would be used by the newly reformed Locust army against humanity in the coming years.

An Awakening of a Riftworm
In the aftermath of the Lightmass Offensive, the Locust Horde reorganized and began to rearm itself in retaliation against the Coalition of Ordered Governments and a Riftworm was awoken in the aftermath of the offensive. Locust High Priest, Skorge, would use the worm as their god and to launch a campaign against the COG by destroying many of their cities within the Jacinto plateau. For several months, COG outposts, positions, and cities began falling one by one as they were being sunked to the Hollow by the Riftworm as the city of Jacinto, the last human stronghold, was on the verge of being next and could fall to the Locust.