I spotted this small wasp on the fence where it was scraping layers of wood for her nest, so it was a female. It is a special species: Symmorphus crassicornis [1,2,3]. This is a rare species in the Netherlands.
She scraped the top layer from the fence, I assume because it is most weathered therefor softer and easier for her to use. She rolled the scraped material into a ball while scraping. When she had collected enough she flew away out of the garden, so unfortunately her nest was somewhere else. Everytime she returned she started scraping on a different position.
I had not seen this species before, a new garden species!
A very beautiful wasp with all those yellow accents.
References1 Nederlands Soortenregister
2 Peeters, T.M.J., C. van Achterberg, W.R.B. Heitmans, W.F. Klein, V. Lefeber, A.J. van Loon, A.A. Mabelis, H. Nieuwen-huijsen, M. Reemer, J. de Rond, J. Smit, H.H.W. Velthuis, 2004. De wespen en mieren van Nederland (Hymenoptera: Aculeata). – Nederlandse Fauna 6. Nationaal Natuurhistorisch Museum Naturalis, Leiden, knnv Uitgeverij, Utrecht & European Invertebrate Survey – Nederland, Leiden.