Gateworms are a feature in Call of Duty: Black Ops III on Shadows of Evil. They are required to access the Pack-a-Punch Machine. Gateworms seem to represent an individual's soul, as they are obtained by completing the rituals around the map. Each one is produced by sacrificing a person close to the four characters, one for each character. The individuals are:
If while playing Shadows of Evil in a four player game, the group traps the Shadow Man in the Summoning Key, a giant gateworm will spawn over the ritual altar. Once a player picks it up, the worm is transported to above the Junction District in the intersection of the three train tracks. Killing this worm through the easter egg steps will assist in killing the giant monster that appears in the sky upon finishing the Pack-a-Punch Machine. When the player completes the Fly Trap easter egg and receives the Annihilator in The Giant, My Brother's Keeper easter egg in Der Eisendrache, Seeds of Doubt easter egg in Zetsubou No Shima or the Love and War easter egg in Gorod Krovi, a Gateworm will appear on the image of the map in which the easter egg was completed on which symbolizes that the soul of the Original Timeline character was captured. All four Gateworms and the Summoning Key are required to complete the main easter egg of the map Revelations.
In Revelations, a Gateworm can be obtained by finding an Apothicon Egg and hatching it inside the Giant Apothicon. Once obtained, it can be used to find the four Runes of Creation. When close to a Rune, the Gateworm will begin to emit a sonar ping the closer it is to a Rune.