Trypoxylon figulus - frontal, Heesch, Netherlands
Meet Trypoxylon figulus, in dutch named the "Pottenbakkerswesp" => Pot bakery wasp.
These tiny wasps (8-15mm) don't bake pots yet may visit insect/bee hotels. Initially I figured it to be a sawfly or other parasite, going for the bees. Instead, it's simply a resident of the hotel. They hunt for tiny spiders and stuff their room in the hotel with as many as they can, for their offspring. The finishing touch is a layer of clay, to seal the hole. Pot baked.
Some people have documented both males and females completing the sealing, which is highly unusual for wasps where males do absolutely nothing for their offspring. Males are born much earlier than the female, as soon as the females exits her nest of birth, she's immediately overwhelmed by males wishing to mate.
Their venomous sting is described as to almost instantly paralyze the spider. It needs to be this strong as this wasp is not immune to the spider's bite.
It's in dutch, but this excellent article has many photos of their life cycle, scroll down to "pottenbakkerwesp".
Trypoxylon figulus is a wasp in the Crabronidae family. All Trypoxylon species that have been studied so far are active hunters of spiders, which they paralyse with a venomous sting, to provide as food to their developing larvae.