Bombyx is "cultivated" silk--that is, silk from domesticated silk worms usually raised indoors and hand-fed--as opposed to the wild Tussah silk.
What I have here is silk noils. Noil is the short fiber (or snarls) left over after processing the silk fiber. It is super cheap--basically because it is just waste fiber. It gives sort of a nubbly tweedy look to yarn.
For my continuing alphabetical fiber game, I plan to combine this with Bombyx with Angora. Kind of a crazy combination--but that is exactly the point of this ABC fiber adventure. Stay tuned!