A couple days ago a wren was sitting on a branch above its nest in our wren house. A large ground hornet (cicada killer) was hovering about a foot in front of it. They were face-to-face and the wren was making a chattering, scolding noise. The wren stopped chattering when the hornet flew off. Would a ground hornet sting a wren?

I have no idea, but it does sound like the hornet was interested in something. The wrens in my area are smaller than a chickadee but they don't take much crap from bigger critters.

Seems like the little wrens are just too busy to be bothered with other stuff, they are always busy.