Fireflies are cool!

So I've been devoting a half hour between 2 and 3 am to watch the fireflies in my barkyard. Thanks to a small wood in the backyard they are quite prolific. It's like Christmas. I never knew they like woods, I thought they were mostly grass bugs. I also wonder how these little guys got their light up butts in the first place. With the cool breeze and the twinkling lights I twist in my bed to get the best view, though eventually I have to resume normal position and go to sleep.