Last year I found a number of nesting digger wasp species on a dead branch of a Butterfly bush (Buddleja davidii), among others this Stigmus pendulus. This year there is again a lot of activity on the branch including this female Passalocus corniger  that builds her nest in an abandoned borehole.
The dead branch contains many boreholes with a diameter of about ±1 – 2mm diameter, possibly created by beetles from the genus Anobius as one specimen was present at the moment of observation of the wasp.
The nest with a diameter of 1,5mm is located higher on the branch where the majority of the boreholes are.
At the moment of observation the nest had already been filled and the wasp started closing the entrance. She collects resin elsewhere that is transported to the nest between the mandibles. Using the jaws the resin is spread in layers across the entrance until it is closed..
Around the entrance a number of irregular blobs of contaminated resin and some very round balls of the material are collected that she does not use.
After the entrance is closed the wasp collects wood pulp from the direct vicinity and presses it into the soft resin.
After closing the nest she kept returning to the branch and found an empty borehole to sleep in.
References1 Nederlands Soortenregister