The glow worms are really very tiny insect larvae.  They hatch in dark places and hang long threads down below their abdomen (like a spider web).  Flying insects are attracted to the bioluminesence glowing from their butt and get stuck in the thread.  They are then hauled up to the larvae and eaten!  Kinda takes the fun out of the pretty lights doesn't it?  This photo of the webs was taken outside the famous caves during one of our walks.