Now that I’m aware of the existence of the Gelis wesp, see here, all ants in the garden are suspects. Scanning the ground for early insects awakening after the winter I notice a very small ‘ant’ crawling on a stone wall. And for sure it has an ovipositor. It manages to escape in a gap between the stones. With the sucker still ready in position but without hope she will appear again I give up after 20 minutes. At that moment a larger ‘ant’ comes crawling up a leaf behind the wall and it is immediately clear to me it is a Gelis. The sucker doesn’t fail so the identification process can start.
It turns out to be a female Gelis spurius [1,2] (confirmation Paul Hoekstra), a common species.
References1 Nederlands Soortenregister
2 SCHWARZ, Martin. Revision der westpaläarktischen Arten der Gattungen Gelis Thunberg mit apteren Weibchen und Thaumatogelis Schwarz (Hymenoptera, Ichneumonidae). Teil 3. na, 2002.