I'm GM'ing a game with a large, mostly mundane party where all PCs at level 2. The party is made up of a good aligned cleric (i.e. no damage spells), wizard, druid (with wolf animal companion), monk, barbarian, rogue, and ranger.
My story is centered on an Order of Monks that worship a local parasitic wasp so the type of creature is particularly relevant and kind of hard to avoid. The upcoming session is the one where I plan to introduce the wasps and I had wanted it to be a surprise.
If I take the wasp swarm right from the Pathfinder bestiary, as far as I can tell, it would destroy the party. The wizard is the only one who can damage the swarm (as the swarm is immune to weapon damage). Even if the wizard were only to memorize damage based spells he wouldn't be able to do enough damage to kill the swarm without some higher than usual rolls.
I'm considering having an NPC from a town provide the ranger with a small quiver of some kind of arrow that does fire damage and a warning about the wasps. This isn't the way that I had hoped to introduce the wasps as it ruins the surprise.
Is there any other way that I can tailor the encounter to make it something my PCs can handle or am I overlooking some of their classes abilities that can get them through it?