What the he** is that?!

When I stepped outside today several of these enormous flying bugs were circling the flowers by front door. Sophie decided she needed to catch one though I though we should all just run away! These things are the biggest bugs I have seen outside of Brazil! Evidently they sting too as Sophie quickly found out! Can anyone identify what these are???!! I'm not sure the photos do them justice. The largest ones are about 3 inches or more!! They are like bugs out of a bad horror flick!