Learn Italian: Le farfalle sono più belle delle mosche. - Butterflies are more beautiful than flies.

You can attach the pejorative suffix -accio to the noun. Mosca (fly) becomes moscaccia, so in the plural, you would change mosche to moscacce.

If we wanted to talk about "cute little butterflies," how would we alter farfalle?

You would use a diminutive suffix like -ino. You drop the final vowel of the base word and add the feminine plural suffix -ine to get farfalline.

Why do we use delle instead of just di for "than" in this sentence?

When comparing two nouns using più ... di (more ... than), the preposition di must combine with the definite article of the second noun. Because "flies" in a general sense takes the article le, di + le combines into delle.

In English we just say "Butterflies" without "The". Why does Italian use Le here?

Italian requires definite articles when talking about general categories or broad concepts. Since we are making a general statement about all butterflies, we must use Le farfalle rather than just farfalle.