Brood Hosts are specialized Hive Knights seen in the Broodhold Strike, where the Knights can be seen protecting their nest in the Hellrise Canyon and the Broodhold itself. Given a Worm corrupted by Ether, the Knights are both empowered and poisoned by the adverse effects of the alien substance, granted increased resilience and strength while responsible for feeding the volatile Worm inside them.
Trivia
In the Ordeal variant of the Strike, the Brood Hosts are replaced by Barrier Knights, that function just like them, including carrying the tainted Worm, except it has the Barrier ability.