Thanks J (and thanks for the acorns)! From what I've read, Zebra Longwings are one of the few butterflies that roost together like that. I've seen them do it several times before, but this seemed to be the biggest cluster I've seen. We do have a lot of them in the flight cage right now so that's one reason, but I think the cooler weather might have something to do with it, too. The downside of it is, sometimes a lizard or a frog will get in the flight cage and the boss has walked in to find "mass carnage" of Zebra Longwings. They sleep (or whatever it is butterflies do) really deeply. I've read you can pick them up and move them to a different location and they don't even realize it or move (I haven't personally tested this theory yet). So they're kind of like sitting ducks and it doesn't help when they're all together and some predator finds them. Luckily, our screen has been holding up lately, although the boss is looking into getting it replaced.
