This is a selection of photos of the last couple of weeks.
A pair of Osmia rufa. Apparently, the male stays on top of the female for a while after mating. Note the smaller size of the male and the 'horns' on the face of the female
A bee about to leave the nest. It looks like a male
Another male inspecting a hole
Female starting to build the last cell wall
The wall is almost complete
The finishing touches
The finished nest
This little fly - same size and family than the fruit fly - is a cleptoparasite of Osmia rufa nests. It lays its eggs on the stored pollen in the cells.
Links: Solitary bees
An article with interesting photo of the inside of the nestAnother article with lots of info on associated fauna to Osmia rufa nests