If you have, or visit, a home street with multiple firefly hives, and they are spawning way fewer than 10 fireflies/hive, that means one or more of the hives needs restoring. BUT! In my experience, every firefly has to be gone from the street before the hives that need restoring will go "poof!" This is easy to achieve if there are only two hives or if most of the hives on a street need restoring at the same time. So if you're interested in the iMG from restoring resources and have a little energy to spare, consider whistling for partially-full jars to clear out the local population so they can start fresh. If there are too darned many hives around for you to catch every last firefly before the healthy hives respawn, consider enlisting a few of your fellow Glitchen for a simultaneous harvest and that should give the 0% hives a chance to collapse.
The more you know :)
ETA: This was written from a route-curator's perspective, so that whole thing about restoring other people's hives ... well, I haven't heard objections to doing it on the Fireflies & Barnacles Route. I can't & don't speak for any other Glitchen.