Corey speculated that it might be the work of a wasp, because wasps are good at carrying stuff; I had a feeling it was a bee, perhaps like the potter bees that invade my greenhouse and have twice filled every gas jet in my space heater with CLAY rendering them UNUSABLE. No more of those please! Wasp or bee, it was dang cool, this series of little nectar and pollen-stuffed grub cigars hidden way down the side of a fuchsia pot. I hated to disassemble this careful creation, and never meant to. So after opening one to figure out the story, I carefully placed them along the side of one of my hanging baskets, hoping they'd be OK and hatch out.
It didn't take long for Corey to come back with the answer: I'd found the work of a female leaf-cutter bee, genus Megachile. These harmless little bees look like a blackish honeybee with a yellow underside. In fact, they gather pollen and deposit it on their extra-furry bellies, which is pretty charming.
I couldn't do better than Beatriz Moisset's lovely writeup on the U.S. Forest Service's website.
January 9, 2016: