Answer:
The correct answer is una metáfora.
Step-by-step explanation:
A metaphor is something very common used in poetry and other literary genres.
Its function is to compare two things aesthetically.
In this case, beautiful women are being compared to butterflies.
Words are written in an aesthetic way, they are pleasing to the reader's view.
The metaphor can be confused with the simile, but for this sentence to be a simile it should say that women are like butterflies, and it does not say so.
In the metaphor two different things are compared, but they have some kind of similar characteristic. In this case, women and butterflies have the characteristic of being beautiful.
Given this information we can say that the correct answer is metaphor.