Earlier this afternoon, I was sitting reading on the sofa in our living room. The window was open and the sunshine was streaming in. The book I was reading was The Master and Margarita by Mikhail Bulgakov. I had to get up once to guide a bluebottle fly out out of the window, but soon got back into the book. A bit later I slowly became aware of a buzzing sound, like that of a wasp, but not quite right: too even in volume. Then I realized: not a single wasp but lots of them! I jumped up to look out the window. There were thousands of wasps in the air, orbiting each other like a cloud of giant midges. I rushed round the flat closing all the windows (probably unnecessarily, as they didn't seem to be interested in coming indoors). Slowly, they rose up and moved over our flat roof, and I watched from the kitchen window as they drifted off towards a tree near the main road. The swarm was about 3 to 5 metres in diameter, with occasional members much further away. I last saw them above the path beside the road. Strangely enough, people walking along the path didn't seem to notice them at all.