One thought that occurred to me while looking out the window and watching them flash in the night....
I had previously thought that fireflies only bred near a stream/fresh not stagnant water source, and wondered where the fireflies that come to my garden came from. Nearest open water is a tiny creek that has been corralled into a ditch drain beyond the woods behind my property, then sent underground as storm drain below streets of my development until it emerges about 1/2 mile away on the other side of the development and flows into a large pond/tiny lake.
...now that I've recognized the "weird pink shrimp like thing" as firefly pupae and see them often when I'm preparing for spring planting, I know that the ones flying in my garden at night are likely newly emerged permanent residents that have been working in the Garden Patrol for years, and after a summer of courtship, laying the eggs for next generation right here in my garden.
and are really beneficial insects except they do eat earthworms. 
(...and there are earthworms to spare in the garden -- I don't mind if the fireflies eat some. 
)
