- "Anya, it's a giant worm! They're sinking cities with a giant worm!"
- —Marcus Fenix to Anya about first seeing the riftworm for the first time
The Riftworms are a species of massive, subterranean worms. Reaching a confirmed maximum length of 10 miles and width of half a mile, it is the largest and oldest animal known to have existed on Sera. Semi-intelligent creatures, capable of century-long hibernation, Riftworms created the Hollow, a complex underground network of tunnels, by burrowing through the crust of Sera. Leaving a rich manure in their path, it fertilized the soil and created life within the Hollow. The Riftworms were viewed as Gods by the Locust Horde, a race of mutated humans created in part from the Riftworms, for being givers of life. Thus, their main religion based on the Riftworms, known as the Trinity of Worms, was formed. Only three Riftworms have been known to exist. During the Locust War, one was awakened and used by Ketor Skorge as a weapon of mass destruction, capable of sinking entire cities. The last known Riftworm was killed in 14 A.E.
Riftworms were gargantuan, worm-like creatures that could grow ten miles in length. They burrowed across the Seran crust, devouring everything in their path and leaving behind a rich manure. The manure then fertilized the soil within the tunnels, later termed as the Hollow by humans, and created life underground. An ecology of plant and animal life evolved in the Hollow, with many of the creatures being reptilian in nature, like the Riftworm. Among the lifeforms created in the Hollow by the Riftworm was Imulsion, a parasitic fungus that was capable of infecting, mutating, and possessing any living organism. At some point, the Riftworms went dormant in the Hollow.
The Imulsion created from the Riftworms would eventually become a fuel source by the humans, who were unaware of Imulsion's true nature. The mining and refining of Imulsion led to many of its miners and their families infected with a fatal condition known as Rustlung. The Coalition of Ordered Governments, a relatively new global superpower due to their occupation of Imulsion, feared the reaction from the public if it was discovered of Imulsion's health effects. Thus, the New Hope Research Facility was opened in secret to house the sick children of Imulsion miners and treat their Rustlung.
The Director of the facility, Doctor Niles Samson, began administering regular doses of Imulsion injections to the children to study its effects. He discovered that while Imulsion caused immediate cell stress, it also led to possible point-mutations. Regular biological countermeasures failed. It then came to his attention when a female child named Myrrah had high doses of Imulsion but no ill-effects. Rather, she benefited from Imulsion exposure with it strengthening her immune system and decelerated her aging by 50%. Dr. Samson attempted to replicate Myrrah's immunity but had no success.
Imulsion proved, however, to carry out genetic engineering through its mutagenic nature. Dr. Samson theorized that the indigenous creatures of the Hollow were genetically immune to Imulsion, due to their proximity in nature and showing no ill-effects. According to the Trinity of Worms, Dr. Samson discovered the Riftworms. He extracted their genetic material and combined it with Imulsion to mutate the children's immune system. The children instead were transformed into genetically unstable, distempered, sterile, and aggressive creatures Dr. Samson called the Sires. He then believed that the Sires were the next step in human evolution and could even have military potential to help end the Pendulum Wars.
Eventually, his unethical experiments were discovered by Chairman Monroe and was shut down. However, a shadow government within the COG believed in Dr. Samson's work and relocated him, his subjects, and his remaining loyal scientists to another facility hidden in Mount Kadar. In the facility, he continued to perfect the Sires by making them genetically stable, healthy, and able to reproduce. He then used the embryonic stem-cells of Myrrah with the DNA of the Sires to create the Locust Horde. Myrrah later had a human daughter named Reyna with scientist Dr. Torres, but was led to beieve that Reyna died when Dr. Torres fled the lab with her.
In Myrrah's grief, she used her telepathic control over the Locust, known as the Hivemind, to rebel and slaughter the scientists. Myrrah, taking the role as the Locust Queen, led her people into the caverns of Mount Kadar to build their own civilization: Nexus. The Locust learned that their evolution was due to the genetics of the Riftworm, and that they were sustained by the life in the Hollow also created by the Riftworm, and thus saw the Riftworms as gods. As they created their civilization, they build a religion around the Riftworms known as the Trinity of Worms. The architecture of the Locust was also based on worms in tribute to their deity.
During the Lambent War, many of the Locust came to believe that the Trinity of Worms never existed or were long dead and unable to help them. During the Assault on the Temple of the Trinity, Vold Karn suggested awakening the Riftworms to aid them against the Lambent.
In the fourteenth year of the Locust War, after the Lightmass Offensive, a single Riftworm was awakened by the massive explosion of the Lightmass Bomb. High Priest Skorge would use their god as a living weapon of mass destruction to begin a campaign on destroying Seran cities on Jacinto Plateau. For several months, COG outposts and two cities along the plateau vanished, forcing the COG to venture into the deepest areas of the Hollow to kill every single Drone to end the war.
With the assault on the Locust tunnels in the Inner Hollows, Delta-One was ordered to investigate seismic activity near, and beneath, the city of Ilima. After Delta assisted a Gear squad by killing the Locust's mortar crew and using their position to attack the Locust, Marcus, Dom and Carmine noticed that the "wall" was moving, and they realized that whatever was moving was the source of the seismic activity.
After getting through Locust defenses and opening a gate, Marcus, Dom and Carmine took cover as they noticed the "big shot" ride a Hydra and scream unintelligible language. The Riftworm then appeared and began sinking Ilima, and the Gears learned of its name and deduced that it had also sunk Montevado and Tollen several months ago.
The Riftworm would circle around the Ilima sinkhole, continuing to destroy it. Later, as Delta-One rescued Baird from Processing, they managed to signal a King Raven to pick them up. As the King Raven picked them up and began to leave, the Riftworm burst out from the ground and swallowed it.
- Main article: Destruction of the Riftworm
- "First we kill it, then we cut our way out!"
- —Marcus Fenix, deciding to kill the Riftworm from the inside before escaping it.
After recovering from the crash/swallowing, minus a missing Carmine, Delta battled their way through the worm, in an attempt to find its heart and kill the creature. Narrowly avoiding the many digestive systems in the Riftworm, they found Carmine but they were too late, as his stomach was already eaten by the Riftworm's secondary digestive system, the Nemacytes. In anger, Cole shot wildly, which resulted in the Riftworm sending a wall of debris down.
Delta Squad narrowly avoided getting crushed by the debris, and passed through several lethal obstacles that were part of the Riftworm's systems. They later encountered the heart and severed its arteries, but the Riftworm still continued. Baird deduced that there was more than one heart, and the Gears followed the sound of the remaining hearts and severed them.
After severing the third heart, the beast erupted out of the Seran crust a mile into the sky from a heart attack and massive loss of blood. It roared as it spat out gallons of blood and crashed to the ground dead. The Locust's advantage in the war was destroyed.
Delta cut their way out of it with their chainsaw bayonets, and were shot out in a stream of the creatures blood, narrowly avoiding drowning in it.
Following the death of the Riftworm, the Locust plan was delayed, but not completely foiled. During the Siege of Nexus, Queen Myrrah could be heard broadcasting that even though the Riftworm is dead, the Locust plan to sink Jacinto continues.
If there were any other remaining Riftworms in Sera, their fate remains unknown after the flooding of the Hollows and the Imulsion Countermeasure Weapon's activation. Its possible that they drowned in the flooding of the Hollows since they wouldn't have been awake to escape.
After 17 A.E., following the end of the Locust War, a group of Outsiders, people who reject the new COG, built a village within the skeletal remains of the Riftworm calling it Riftworm Village. It later came under siege from the Swarm and was defended by several members of Delta Squad, the very people who killed the Riftworm in the first place.
- The Rise of RAAM (Photo only) (Mentioned only)
- Gears of War 2 (First appearance)
- Jacinto's Remnant (Mentioned only)
- Gears of War 4 (Mentioned only)
- Ascendance (Mentioned only)
- Gears 5
- Bloodlines (Mentioned only)
Behind the scenes
- The Riftworm makes several appearances before its debut when sinking Ilima. The Riftworm is first seen before the first encounter with the snipers, in the tunnel filled with yellow fumes, with the Riftworm slowly moving on the left side. Then, it is seen again after saving the Gears squad from the heavy mortar fire.
- Inside the Riftworm, Delta Squad comes across the bodies of four Gears and one civilian, not including that of Benjamin Carmine.
- When the player passes by the Riftworm's digestive teeth, Dom will ask if the large hanging organ in the area is the heart, but Baird says no. If shot at, the worm will moan and gag, meaning it must be the uvula. Which explains why Cole's excessive shooting of it caused a wall of debris to fall through the worm's throat.
- Due to its continuous internal organ system and multiple hearts, the Riftworm anatomy may be based on the anatomy of real-world Earthworms.
- The Riftworm being a gargantuan, prehistoric creature in dormancy and then being awoken by the Lightmass Bomb is very similar to the monster Godzilla, which is also a gargantuan, prehistoric creature in dormancy and was awoken by the atomic bomb.