Final answer:
The lines from Dante Gabriel Rossetti's poem use simile and metaphor as figures of speech. The dragon-fly is compared to a 'blue thread' using a simile, and the sky is metaphorically suggested as fabric through the idea of the thread being 'loosened from the sky'.
Step-by-step explanation:
The lines from the poem by Dante Gabriel Rossetti illustrate simile and metaphor. A simile is shown in the comparison of the dragon-fly to a "blue thread" using the word "like", suggesting a delicate, thin appearance akin to that of a loosely hanging thread. The metaphor is presented through the idea that the thread is "loosened from the sky", suggesting the sky as a fabric from which the dragon-fly is a part. Although there is a strong use of imagery in these lines, there is no evidence of personification, metonymy, synecdoche, or irony.