Since the question is asking which noun is the subject, the subject would be the Ladybug because it fluttered from one leaf to the next. And the only other noun would be the Leaf, because its a thing. But I don't think the leaf is the subject. So therefore its the Ladybug.
The element that Dante’s Inferno shows to the reader
about the corruption in church is wealth. He believed that the root of all evil
(especially corruption) is wealth. Thus the reason for all the money and
greed-based areas in Hell.