At first I thought Trichrysis cyanea (for me 'the usual (blue) suspect' on my insect hotels). I would like to know if an id is possible. I don't think it's a (Tri)chrysis now after a more closer study of several blue Chrysididae. The head is more square and it's not a match in body type. The abdomen seems less punctuated than I normally see in T. cyanea. But what can it be otherwise than T. cyanea. T. indigotea is very rare in the Netherlands. I have never seen it, it's not likely so the usual suspects are to expect.
Date: today, 23/7
Size: about the same as C. ignita group members on my insect hotels, maybe slightly smaller (about 0,5 mm smaller, I'm not sure).
Location: my garden, The Netherlands southern part on one of my 16 insecthotels.