The significance of the moth is change. Caterpillar into chrysalis or pupa... and, from thence, into beauty.
11 seconds sound clip from the The Silence of the Lambs movie soundboard.
You can hear this line at 00:55:52 in the Blu-ray version of the movie.
Quote context
[...]
- Now, that hasn't been made public yet.
- We don't know what it means.
- Just like the one we found in Benjamin Raspail's head an hour ago.
- Why does he place them there, Doctor?
- Our Billy wants to change too.
- You're so close to the way you're gonna catch him. Do you realize that?
[...]