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, Juho, et al. An illustrated key to the cuckoo wasps (Hymenoptera, Chrysididae) of the Nordic and Baltic countries, with description of a new species. ZooKeys, 2015, 548: 1.