I was delighted to find several of these beautiful big female wasps today. This one was ovipositing into a Beech tree snag. The long whip-like appendage you can see going into the tree can look like a big stinger when it is trailing behind her. But these wasps are incapable of stinging.

Bug guide gives the female's size as: "females 35-75 mm (body), 50-110 mm with ovipositor". This female was considerably larger than the other female who had been ovipositing earlier. Males are not seen nearly as often as the females.