Good news, though: Yesterday was sunny and nice, and I did manage to take a few photos of the aforementioned red-listed little bee. No glorious photos, but decent enough to tell that it really is Andrena hattorfiana:
You can tell the species by the colouring of the abdomen - and the fact that the lady is gathering nectar and pollen from a specific flower genus, the Knautia flowers. Which happen to grow on our not-lawn...
Here's a second shot of the bee:
And as a bonus, an European peacock (Aglais io):
Actually it's two of them, one with closed wings is sitting right on top of the summer lilac flower.