I didn't know which Andrena (mining bee) species it was until I looked it up at home. I am very grateful to Louise Hislop, our local wild bee expert, for confirming that it is Andrena scotica. The only bees I saw were females. They are about the size of worker honey bees and have a characteristic black and white scopa (pollen brush) on the back leg.
Unlike many mining bees which each have a separate nest entrance, several Andrena scotica females share an entrance and the individual nests branch off inside the wall.
This one is resting in the entrance before going foraging.
These are returning with full pollen loads.
Like many solitary bees, this one is mostly known by its scientific name. I get the impression that rather than being traditional, many common English names have been made up fairly recently. This one is the chocolate mining bee, presumably because of its colour, not its taste.
Here's another bee I had to look up when I got home. It is obviously a Nomad cuckoo bee and is Nomada marshamella. It is a cleptoparasite, meaning it lays its eggs in other bees' nests, and its typical host is Andrena scotica so it was no surprise to see them together.
Unlike last week's bee, Nomada goodeniana, which had green eyes, this one has red eyes as well as different colouring and patterning on the body.
Cuckoo bees don't collect pollen and so have no pollen brushes and are much less hairy than their hosts.
They do forage for nectar but spend most of their time lurking outside their hosts' nest holes, waiting for the opportunity to sneak in and lay an egg.
Then I saw a third bee, another first for me. It was tiny, only around 5mm in length. I managed only this photo before it flew away. It has a metallic green-gold colour and a pollen brush (scopa) on its back leg, so is a female.
After searching through Steven Falk's Field Guide to the Bees of Great Britain and Ireland I decided it must be a Lasioglossum bee. I sent this photo in to the BWARS (Bee, Wasp and Ant Recording Society) Facebook page and I am grateful to Stephen Boulton for confirming this. He says it is one of four species the Morio group which can't be separated by photo so it is just a Lasioglossum species. It is the smallest bee I have seen so far.