The little "poopers" that Henderman mentions are most likely caterpillars, and judging by the size of the chewing and the size of their poop, they should be quite visible. They will probably be a shade of green — might match the plant, so look closely. There could be several sizes. One way to find them is to brush away all the poop in the evening (it is actually called frass), then check first thing in the morning. Find the new frass and look directly above it. With luck, the culprit will be munching above where its dropping landed. Good luck!