The third solitary bee home that you can just barely see in Coco's second picture above, was build by Leif at our PEP1 gathering last month!
He completed a PEP BB for it
here and posted these photos of the elegantly simple design:
Built a mason bee hotel today, from scrap 1x4s and finish nails, using a hand saw to cut the chunks of board. The reeds were courtesy of Jocelyn, and it was mounted today to the base camp garage!
Thanks for another bee hotel, Leif! Ours has been filling up each summer!
Note that the common term for solitary bees is "mason bees" though mason bees are just one of many, many types of solitary bees. Mason bees pack their nesting tubes with mud and are more prolific and common in slightly warmer zones like the Pacific coast. If I recall, mason bees hatch in the spring, when temperatures are consistently above 50F or so during the days.
Leafcutter bees pack their nesting tubes with--you guessed it--leaves(!) and are more common and prolific
inland where the summers get hot and there are colder winters. They hatch in late spring or summer, only after several days in a row of 70F or above. Leafcutter bees prefer a smaller sized hole than mason bees, too, I think.