Swampy grew quite a bit (that's why I'm even considering that it might've still been a 4th*), then we had a hot sunny day, I wanted to give it a bit more vent, and accidentally left a wide enough gap for it to escape!
I kept on a lookout for Swampy, of course, but it wasn't until yesterday morning that I found it... hanging as a chrysalis on the wooden pole curtain rod!! I'm SOOO relieved we didn't have a cloudy or rainy day while Swampy was missing because I would've flung those big wooden ring hung drapes wide open! I'll spray Swampy off of there tomorrow and pin it up in the eclosing cage.