Dangerous Stranger

During our walk with Omo, I spotted a smal place with colourful wild flowers. Obviously the farmer has forgotten to poisen it. 
I returned in the afternoon with the camera to blip something blue for Tiny Tuesday. There was a lot going on. A lot of different insects enjoyed the diversity. I like this obviously very dangerous stranger. The bee was very impressed (first extra) and decided to chose another bloom.
In reality it is a harmless fly with a great defensive strategy (second extra)
I try to find the name of the fly asap. Now I'm too short of time to search for it in the www. Any ideas?
Intothehills mentioned that it could be a Physocephala and I think it is a Physocephala nigra. Than I was wrong with my suggestion that it is a defensive behaviour. I found this in Wikipedia:
"The bladder flies are parasitoids, they develop in various other insects. Their main hosts are bumblebees and wasps, more rarely furrow bees and grasshoppers. Many species are relatively unspecific in the choice of their hosts, and the size of the animals of the same species varies accordingly. The eggs are laid in flight on sedentary or slow-flying host animals. The larvae hatch and invade the abdomen of the hosts who eat them up. The wintering takes place in the dead host."