Invisible creature and swarms

[Lobolusk]

What Happens if you summon a insect swarm into the same square as an invisible creature damage wise for the invisible creature?

[R2D2TS]

The swarm will do damage as per the swarm attack trait of the swarm subtype. Swarms are not subject to miss chance from concealment or cover. The amount of damage is based off the HD of the creature, unless the summon ability gives a damage listing of its own. You can find all this in the Bestiary section for subtypes. Just look for the Swarm subtype. You can also check the PRD.

[Xaratherus]

Swarms can be summoned (knowingly or unknowingly) into a square occupied by a creature.

They don't deal damage until they actually end their move action in the square, though, so the real question would be whether or not the swarm would realize that it was already around\on a creature?

Since a lot of insects, and the creatures under Summon Swarm, all have a way to 'get past' invisibility (scent, tremorsense, or blindsense), I'd guess they'd be aware of the invisible creature and would just stand in the square and chew on it.

And in the meantime, you'd see a swarm-covered nothing dashing around trying to get rid of the bugs.