If Finder of Paths Unseen uses Infestation of Venomous Spiders with threshold, when does it have to pay for Responsibilities of the Dead?

If Finder of Paths Unseen uses Infestation of Venomous Spiders with threshold, when does it have to pay for Responsibilities of the Dead?

Each time an action is skipped and 1 or more Invaders are destroyed by the Damage (from the resulting triggered action).