What kind of bug could this be?

I was just outside (its a little bit after 10pm here) and something bit the backside of my thigh..and HARD! I smacked whatever it was away, and it flew off..slowly...slowly enough so that I could get a pretty good look at it. It was large, maybe 1 1/2 times the size of a horse fly..but wasn't a horse fly..or a fly for that matter. It had a stinger on its backside that had to be close to 1/4 inch long **rubs leg in pain.** It made a humming/buzzing sound when it flew. What could this beastie be??