Cavir is a planet populated by feral zerg.
Daggoth used the planet as a birthing colony for his Tiamat Brood. After the death of their master, the zerg became feral and fought each other. During the Second Great War, Abathur discovered a small group of lurkers among the survivors.
Sarah Kerrigan was able to control the group of lurkers, but couldn't morph more of them. Abathur informed her that a key sequence was missing, and that a lurker den was required. One was found nearby and the group of lurkers was used to protect it from more feral zerg until Broodmother Kilysa arrived to recover its essence.
At some point between the End War and Brood War, the planet was re-visited by the rogue brood of Abathur and Mukav, who were plotting against Overqueen Zagara. The anub'alisk, which had been created to safeguard the colony, was incorporated into their brood.