If you are finding them in the veggie patch... I think that tomato horn worm (manducca sexta) is likely.
They're not the gorgeous hummingbird moth...
But they are still very cool.
I took some pictures last year...
http://gardens-in-the-sand.blo...
When I get caterpillars on the tomatoes, I might move them to the datura... Or to the black nightshade... They will often show up on the alternate host plants without my help.
