Well, till now, we've been following tracks that had a beginning and an end. Not for Bombyx. His tracks look just like smaller silweed plants! And since silkweed grows on the borders of the waters anyway, you'll get a bit of a hard time tracking him down.
Bombyx roams the general middle area north of the Temple of the Red Crane, about where the lake splits into two rivers. I have not included a map with his path, this is because he is confined to a relatively small area, and turns and circles and pauses along this path! What I suggest is just throwing flares down where you see a lot of his tracks.
This is a rough map of his whereabouts:
And here is a video by Kalliope featuring Bombyx: