A male Blue mason bee (Osmia caerulescens)  hangs around the bee the lower parts of the bee hotels, sections 3 and 4. He rest often on top of section 3, the upright stemm.
Every now and then he will fly to the small stemms in the lower part of section 4, to rest and observe the outside world.
Fortunately one of my favorite bees, the Blue mason bee has returned this year. This male is inspecting and defending potential nesting locations, in section 2. Despite the is fanatical in chasing away the larger Red mason bees.
References1 wildebijen.nl, "De Nederlandse bijen en hun relaties, overzicht van in Nederland en Vlaanderen voorkomende solitaire en sociale bijen (Apidea s.l.)"