Last Spring I hung a bundle of hollow twigs sealed at one end in hopes that some bees would take residence inside them but no bee accepted the offer. Last July I was surprised to see a flying piece of straw and then I realized what was powering this flying object, a grass carrying wasp, of course. The busy mother tucked the piece of grass in one of the holes. I left on a trip so I couldn’t follow her comings and goings as I would have liked.
Finally I decided to split open the hollow stem (the only one with something inside). She had plugged the sealed far end with additional straw (far left), the cocoon came next and finally to the right there was some loose straw, most of which fell off when I opened it.
A close up of the cocoon (second picture) reveals something that I only noticed when I saw it on my computer screen: the remnants of the grub’s meal, legs and wings of some Orthopteran (a katydid perhaps?).
The cocoon itself was made of three layers, the exterior one, partially removed on the third picture, was a loosely woven web, the next layer was more tightly knit and the inner one was a very thin and dark membrane that appears waterproof.
I had caught a glimpse of the mother when it was building the nest, perhaps it was the same species as:


Higher resolution image