A malee Gasteruption erythrostomum , a carrot wasp, on the bee hotel.
The females are permanent residents in the garden, but the males I had not yet seen.
Male Carrot wasps are recognisable by the absense of the ovipositor on the tip of the abdomen.
References1 Kees van Achterberg, 2013. "de nederlandse hongerwespen (hymenoptera: evanioidea: gasteruptiidae)"