Rock Worm

The Rock Worm was a creature that lives in the Hollow. Described by Anya as "an indigenous cave creature," these large, worm-like organisms slither from one tunnel to another, eating the glowing red fruit growing on the cavern walls and ceiling.

History

 * "Our enemy talks to worms. if they're outsmarting us in this war, then we probably deserve to be extinct."
 * — Damon Baird on the Locust religion.

In Gears of War 2, it is revealed that Locust hunt these creatures for food. It is speculated that the Locust also use them to make their clothes and armour. Kantus priests can control Rock Worms and Tickers with their strange chants. As part of the Locust hunting ritual, a Kantus would lure a Rockworm out with these chants for Locust hunting parties. They would then be slaughtered and have their meat carved up by Butchers.

It is speculated that the Locust also worship them - why is unknown. Various Collectibles, however, refer to a Trinity of Worms and the Riftworm. It may be for their gunfire-resistant hides, for their role in the formation of the tunnels in Sera's surface, or for being a perfect food source. However, they may be completely unrelated to the Riftworm.

Gameplay
Their tough hides are impervious to gunfire, appearing like stone. They'll mind their own business unless you get in their way - if you stand in front of their faces while they eat they will attack you. This usually does little damage, but on Hardcore or Insane difficulties they will kill you instantly. Rock Worms eat a red glowing fruit that grows on the cavern ceiling. The fruits can be shot down to lure the worm to use as cover. You have to keep up with them when they get moving, and will move faster if they are shot in a vulnerable area like the tail. The caverns beneath Sera are heavily inhabited with them. If you manage to lead a Locust Drone in front of one, however, they instantly kill that Drone. 

Behind the Scenes

 * The Rock Worms loosely resemble Polychaete worms, specifically clam worms, and are complete with extendable pharynxes and parapods.