I walked down the garden this afternoon to check the lawn for broken branches and other debris before getting out the mower.  Walking back up the garden I noticed that the air was suddenly full with a swarm of flying insects.  Then I realised that they were wasps, or were they  bees? Whichever, there were hundreds of them and I decided to retreat indoors for a while.

Later the air appeared clear, so I went down the garden again to take a look. I  spotted this heaving, squirming mass hanging from a tree.  An hour or so later they took to the air again so I retreated indoors once again (making sure the doors and windows were closed).  When I went down later, there were a few insects still flying around, but the big mass hanging from the branch had gone.

I don't know whether any blippers can explain this behaviour, but I have never seen it before.