I have been watching these bees since 1 June on an old table top on top of a tree stump. It is in a garden in Surrey. I knew these bees are supposed to nest in old snail shells but perhaps the loose bridle joint of the table has a similar configuration. I have not seen the grey ones, I take to be the males, lately but a red (female?) is always in occupation. They are beautiful bees I'd love to know what they are. I have more photographs.