I've come a across a few places now with 100's of fireflies just in a little 3x3 square underground, I could understand if it was a cave or something but its not these patches of 100's fireflies is within stone blocks (i.e. no air blocks) found quite a few of these.
also me and my friends have setup a town near some water and have noticed a massive amount of of fireflies hanging around the water, I went through and grabbed just over 4 stacks of 99 and still there where loads.
now I do quite like the fireflies that are new our town but just a little concerned about if it will cause framerate issues on lower end laptops etc, is there point that the mobs are killed? like upon server restart or something?
With the fireflies in the ground....again not affecting gameplay just thought I would report it :)
EDIT: Just wanted to say, whoever thought of adding Fireflies is awesome! :D