I'm a bug fanatic extraordinaire. In high school I did two categories in Science Olympiad competition and even made it to nationals. The two categories: genetics and INSECTS.

I think you saw a female Giant Ichneumon wasp. There are a few subspecies in the U.S., and they are all big. Including the ovipositor they can reach over 4 inches in length. Ichneumons are parasitic, they use their ovipositors to bore into wood (usually trees) and deposit eggs on the larvae of other wood-boring insects, especially Horntails. They look downright freaky, but they rarely sting. The adults are most active in the late summer months, so this would be about the right time to come across them (or for them to come across you!). I'll see if I can find you a picture.

'Erie :-)