I was in Abney yesterday and found a mining bee hole with it's little volcano entrance.  As I squatted and waited patiently for the bee to return for a photo an interesting sequence developed.

First a bee came along, appeared confused and went away again, possible because I'd interfered with the ivy above the nest and or there was a big lump of me that wasn't there b4.

Then it, or another, came back and was harassed by a couple of flies that seemed to have an interest in the area.  The flies appeared to be a pair and appeared to be guarding the area.

Then more and more bees started to arrive.  6-8 in the end.  None seemed to go to the hole but they buzzed around me and settled nearby briefly. One or two did delve into the ivy but I'm not convinced any got near the hole.

I was under a flowering bird cherry so good reason for bees to be present but they weren't there b4 and they were at ground level, not feeding in the tree.

It then started to rain so perhaps they had come to shelter but the impression was they may have been concerned about my presence.

I thought mining bees were solitary?

All very confusing

Below: the fly in question.  Small, about 8-10mm.