It's nice to know that the primary supplier and maker of these lines is the domestic silk moth,
Bombyx mori.
While this moth and it's pupae are a bit dull to look at there are some spectacular moths with equally impressive pupae that can have their cocoons harvested to make wild silk.
For some reason my wife likes that one.
The amount of information on the ins and outs of making silk on the web is overwhelming, so if you want to waste a few hours in the quiet contemplation of an insect whose properties established a vast global trading network reaching well back into the distant past just google silk moth etc. for the images and follow the accompanying text.
I liked this picture.
At the risk of pushing the significance of insects in the manufacture of fly fishing tackle to its limits it's also worth considering that the cane rod you're ( perhaps) using to catch a trout that's (occasionally) eating insects is traditionally protected from the elements by the secretions of the lac bug,
Kerria lacca` one of the prime constituents of shellac an ingredient of modern varnishes and a fund of interesting etymological paths.