[Executor Keldain]

But remember the Zer gdon't leave stragglers, they move as a swarm, like the Tyranids of Warhammer 40,000 (who are quite like the Zerg in nature). The entire swarm traveled with the Overmind, with the Tiamat brood as his personal guards and command wing.

Zerus is a burnt out husk along with every planet the Zerg have touched, they don't conquer worlds, they devour them (again Tyranid like in nature), consuming the biomass of the planet and assimilating any useful creature strains.