I think the wording for this trait is just strange and way too complicated to fully understand. If even “experienced mage wars players” like us misunderstand this trait how could they publish something so confusing. Even if it sounds weird, IMO it would have been better with the simple wording swarms are « non living », take only 1 dmg per Hit (except AoE), roll 1 extra die for each Life left, psy immune ...