After reading a couple of posts over at A Passion for Nature about Glow Worms I ended up really curious about some things. Specifically I got thinking about glowing as a strategy when you're a relatively sedate small organism. It makes sense as a strategy for a winged animal, but less so (to me) for an earth bound one. The little bit of reading I've done so far though has shown some explanations (ie. some of them are toxic so it is a form of advertising ("Don't eat me, I taste bad") similar to brightly coloured diurnal animals. And also, in some cases, it is used as a lure for smaller insects, to predate them, similar to lure fish of the dark ocean depths.
But the best thing I found in my brief on-line searching was by far this... the best two minutes you'll have today. The Mills Brothers singing "Glow Worm"