You know I tried this sort of thing in the last couple of weeks, With my short lenses I found it impossible to do. I had to get within 6 inches of the bee or wasp, my front element that is. Most of them seemed Ok with it but they just got bored and flew off before the camera locked focus. On one occassion the insect got angry and I had to fly off.
Nice catch! They are fantastic! One of the best ways to shoot hoverflies is from underneath! If you want to know the biological reasons for this let me know and I'll tell you!