Talk:Fireflies/@comment-24697181-20140721012900/@comment-4738639-20140721164552

It works because of spending gems and goes towards your "Spent Gems" activity.

It says in the notes the best way to spend gems is to buy two Giant Habitats, and then sell them. This way you are only spending 30 gems each day you do this instead of 40 gems, and still getting 40 Fireflies.