This small cuckoo wasp, Trichrysis cyanea [1, 2] is a regular visitor of the bee hotels in the garden. The species is clearly a minority around the other Cuckoo wasp species and often only one specimen at the time is present.
References1 Nederlands Soortenregister
2 Paukkunen J, Berg A, Soon V, Ødegaard F, Rosa P (2015) An illustrated key to the cuckoo wasps (Hymenoptera, Chrysididae) of the Nordic and Baltic countries, with description of a new species. ZooKeys 548: 1-116.