What is the noun ladybug fluttered from one leaf to next?

The noun in the phrase "ladybug fluttered from one leaf to the next" is ladybug.

Here's why:

* Ladybug is the subject of the sentence, performing the action of fluttering.

* Fluttered is the verb describing the action.

* From one leaf to the next is a prepositional phrase describing where the ladybug fluttered.