I'm on NG+ and was determined to save Solaire.
I joined the chaos servant covenant without an egghead, but with the old witches ring (I traded my sunlight maggot from NG with snuggly early on in NG+). I offered 30 humanity and got level 2. I killed the Demon Firesage, opened the shortcut to lost Izalith, and found 8 chaos bugs. I killed them, but got no sunlight maggot. Figuring I must have missed one, I homeward boned back to daughter of chaos, and then took the elevator back. Two more times, and I'm convinced that there was no 9th bug to kill. I didn't cross into Lost Izalith. So I went and killed the Centipede Demon. With him dead, I ran back to the shortcut (still hadn't seen the words Lost Izalith, nor approached the Lost Izaltih bonfire). Again, 8 bugs.
I killed them aggressively without crossing the border into Lost Izalith again. Now maybe I was just running quickly after them and didn't notice him at first, but after killing all 8, there was Solaire, sitting in the tunnel, human, saying the normal "was it worth it?" speech. I didn't have to leave the area and come back for him to appear, so I'm guessing I must have run right past him. Cool, I've saved him, but now I need a sunlight maggot.
I went into Lost Izalith via the centipede room, all the way until I got the area change text. He wasn't near that bonfire, and when I went back to the shortcut, there he was, sitting among the 8 hopping bugs. Killed them again, still no maggot. The dang 9th bug won't show up!
Am I screwed? Does the 9th bug not show up if you enter NG+ with a sunlight maggot in your possession? Did I have to trade it in NG? Anyway, Solaire is alive but I'm dreading Tomb of the Giants without my trusty headlamp.
Any advice on how to get the 9th bug to show up would be appreciated.