Bresh and I wanted to take out SolB named today - I want to finish my walkthrough. We laid waste to everything and ended up stuck on the guano harvestor. It might be worthwhile tweaking his spawn chance - it is currently 10% (or there abouts, I'm not about to really sit down and figure it out).
NPCs composing that spawngroup :
# guano_harvester (10%)
# sonic_bat (30%)
# sonic_bat (30%)
# sonic_bat (30%)