The zergultralisk cavern is a shelled structure in which there are numerous high-radiation deposits and other dangerous substances. It is in this extremely hostile environment that the ultralisk gains its toughness. In addition, it provides all of the genetic coding for the larva to morph into the breed itself.[1]
During the Brood War, the ultralisk caverns could also provide additional genetic mutations for Anabolic Synthesis (for faster movement) and Chitinous Plating (for improved armor).[2]
The ultralisk and ultralisk cavern used by Kerrigan in Co-op Missions. Additional upgrades for the ultralisk become available when Kerrigan reaches Level 13.