Andrena scotica

Here is another bee that lives in a wall.  This is Andrena scotica, also known as the chocolate mining bee, presumably because of its colour.  Although it is a solitary bee, the females nest close together in an aggregation and several in a group share a common entrance to their nests through a gap between the stones.  The first bees I saw on cool morning were males, just hanging around outside.

A few females were popping in and out, ignoring the males and looking as though they were already busy nest building, although none was carrying pollen.  The females have a characteristic black and white scopa (pollen brush) on their back legs.

Like most solitary bees, Andrena scotica is parasitised by cuckoo bees, in its case mostly Nomada marshamella.  This is a female.  I have yet to see a male.