I love solitary bees, and have been actively building habitat for them for over 20 years. I use Bee Binder Boards from Pollinator Paradise, and plant lots of native flowering plants. One time I was watching a Megachelidae bee, who had just come up from it’s burrow. I waited to see what happened next. A short while later the bee returned with a rolled up piece of leaf held in it’s rear 4 legs, and went into the burrow. And I said, Bingo! it’s out gathering ‘wall paper’!! :-D In my state there are around 3-400 species of solltary bees. And they are amazing pollinators. And cool to watch, as well.