Isn't that something else? I know that the Hawk Moth is the pollinator for the Datura, but geez...how big is this thing going to get before I have no plant left? I just want to know if that is what this thing is. I've googled it, and I think it is
If you want to save it and let it develop you could put in a container and give leaves from the Datura, some of those you can spare. The way it won't eat your leader shoots. They also love tomato leaves, it is usually called the tomato horn worm, bur they like datura also, because the plants are of the same family.
I met a man who is a successful accountant now because of hornworms (yes, really!). Hiis summer job as a kid was to pick off hornworms in the tobacco fields and he hated them with a passion. He swore that he would NEVER see another tobacco worm again and put himself to work getting an education so he could get out of the tobacco fields and away from those nasty things!
We call them "green twinkies" here in honor of how the chickens feel about them. They can do an enormous amount of damage. But the Sphinx moth is a lovely thing. Bt var kurd. works on them, and so do the parasitic wasps. Don't kill it if you see white eggs on its back!