A new guest in the bee hotel, Colletes daviesanus, a bee from the Plasterer bees family (Colletes) [1,2,3].
When I started the garden project one of the plants a grew was Tansy (Tanacetum vulgare) as food / hostplant. Later I discovered the existance of this bee species, which made me set the goal to try lure it to the garden. And voilá a few seasons later we have success, a new garden species!
The species nests normally in clay walls but it is known to use artificial nesting help as well [4].
UPDATE AUGUST
The next goal has been reached as well, a female has occupied the bee hotel and started building nests. At first I thought the nests were occupied by a spider that closed it with webbing but then I remembered the use of polyester within plasterer bees.
In the end she created seven nests and shows a preference for holes with a diameter of 6 – 8 mm.

Literature
1 Nederlands Soortenregister2 Peeters, T.M.J., H. Nieuwenhuijsen, J. Smit, F. van der Meer, I.P. Raemakers, W.R.B. Heitmans, C. van Achterberg, M. Kwak, A.J. Loonstra, J. de Rond, M. Roos & M. Reemer, 2012. De Nederlands bijen (Hymennoptera: Apidae s.l.). - Natuur van Nederland 11, Naturalis Biodiversity Center & European Invertebrate Survey - Nederland, Leiden., pag: 291
3 wildebijen.nl, "De Nederlandse bijen en hun relaties, overzicht van in Nederland en Vlaanderen voorkomende solitaire en sociale bijen (Apidea s.l.)"
4 Breugel, P. van., 2014. Gasten van bijenhotels. – EIS Kenniscentrum Insecten en andere ongewervelden & Naturalis Biodiversity Center, Leiden., pag: 145 - 154