The local broodmother on Ignus had recently been killed, and the brood was in danger. Abathur discovered that the native ash worm's essence would allow the swarm host to deep tunnel through the planet's crust. Kerrigan had a group of existing swarm hosts locate and kill an ash worm and then had its essence assimilated. Abathur subsequently created the creeper strain of the swarm host, which could tunnel almost instantly to any location with creep. The creeper itself also generated its own creep when rooted. Kerrigan used these new creeper swarm hosts to defend the hive clusters from the Dominion.