The world is filled with small black beetles of all manners and sorts. Can you post a good close-up picture?

Not a criticism, mind you! ;-) I know how little these things are. One of the most important 'jobs' that some beetles have is that of garbage clean up, or 'recycling', as I like to put it. That makes them highly beneficial. 'Maybe' an improved image would lead to an ID.

Aphid control ... ladybug larva on the right, and the others are aphids being parasitized by a wasp's larvae.

It's an army worm, that makes a moth. They actually DON'T occur in large groups, so I doubt it'll eat too much. They're pretty much generalists - you could put it on another plant and see if it'll eat that one. Sherry