I have been on the look out for this bee since being alerted by Louise a couple of weeks ago. It is a Yellow-face Bee (Hylaeus bee) and is tiny, being little bigger than an ant. I managed to take a few photos of females on Astrantia in the garden.
I could see these are female as they have 12 segments in their antennae (rather than the 13 in males) but I was puzzled not to see any sign of a scopa. (That is the pollen-carrying brush in solitary bees, usually either on the hind legs or under the abdomen.) Then I read that the female Hylaeus bee swallows pollen and carries it to the nest in her crop, rather like other bees do with nectar. Here is the bee "eating" pollen from Sweet William (Dianthus barbatus).
I found the males very difficult to photograph because they fly so fast and very rarely land on the flowers. I suppose they must drink nectar at some time but I didn't see it. They are mostly interested in finding a mate. Here two males are attracted to a female on a flower.
The unlucky one, behind, shows his face clearly enough to confirm he is Hylaeus communis, the Common Yellow-face Bee.
Mating is a very brief affair, watched here by an even smaller something, possibly a wasp.
I am amazed at the variety of bees that have been living in my garden without me knowing and by the many ways in which they live. I'm still looking out for more.