I think we should increase the fire damage to 1d6 fire (the fire elementite swarm at the same CR does 2d6 fire).
It should only get 2 feats, right? Suggested Feats: Ability Focus (combustion), Alertness.
Skill ranks: Listen 2, Move Silently 4, Spot 2?
Don't forget the distraction writeup:
Distraction (Ex): Any living creature vulnerable to a swarm's damage that begins its turn with a larval fyrefly swarm in its space must succeed on a DC 12 Fortitude save or be nauseated for 1 round. The save DC is Constitution-based.