I've been noticing Andrena nigroaenea females entering holes in the stone wall of my house. I think they are holes have been used by Anthophora plumipes and Osmia bicornis in the past. I've always assumed that Andrenas were primarily ground-nesting bees; there is a small colony A. nigroaenea using an adjacent garden area.
Is the use of vertical stone walls by Andrena bees reported commonly? I personally haven't seen other Andrena species doing this. Or could it be that they are just using the holes for "roosting"?