Ah, that makes so much more sense! I thought the shepherd were calling the shroomlings to themselves, but I see that I misread the board. Thanks for clarifying :-)
Even if the faction isn't stable, I like the fact that opponents can see the swarm building (very visually) and decide to do something about it. And as a player of the faction, it will be satisfying to see all your hard work from many turns finally pay off ;-)