I found this beast in the studio the other morning and immediately got my camera out. Not knowing what it was, I posted it on Facebook and was subsequently pointed to iSpot where it was identified as a horse fly!
You have to click on the images to zoom in and fully appreciate the sunglasses. It was about 2 – 2.5 cms in length and had a low, loud buzz like a large bumble bee. I had always thought of horse flies as vicious little expletives, not monsters like this appeared to be. It may just have been a matter of seeing it in detail and out of context, i.e. in my studio and not in the field (where it should have been).