Unlike Swarms from the previous game, Diablo III Swarms do not drain character's resource, but inflict quick Poison damage hits in melee. They have unique ability to pass through any other monsters and most obstacles, and, of course, can fly. Overall, these are very simple enemies, and should not pose a serious threat. In Act III, within a Fortified Bunker, an empowered Plague Swarm variant may be found.