I see solitary bees in my garden but I haven't been able to get any to move into what I offered them. I think perhaps my soil is too sandy for them to be able to seal the ends of the tubes. There is no clay close by. I have a lot more luck with burrowing wasps who keep my caterpillars under control. Army worms and cutworms seem to be their favorite prey. Cabbage worms get worked over pretty good by the yellow jackets.
I don't think it needs to be all that big and fancy. Salamanders seem to enjoy the cheap half a star hotels under a loosely placed piece of half rotted wood, and the bumblebees would so enjoy a sleepy night under the stars on a coneflower.
But, just like myself, never standing a chance of being in a 5 star hotel, it's still nice to know they exist, and see pictures of them!
Oh those are so cool!! That really apeals to my I-can't-throw-this-away-because-I-might-use-it-for-something-someday!! Whether any bees, or other critters moved in, it sure would make a fun project for me and my grand daughter! Plus, it would make a attractive-in-a-weird-way garden decoration. row