I think they stay under 2 feet, and if they get bigger than that it would't be by too much.
I've never known ribbons to eat insects- has anyone actually seen this?
Sometimes I let mine slither around the garden. (he's pretty calm, he wont take off or anything) He goes under rocks and stuff and comes out with a mouthful of slug or spider. So I think they do sometimes eat insects. After all, I think it would be harder for a snake to go out and catch a fish every time it was hungry, than say looking under a rock and eating all the bugs. ~TR~