Silkworm gut used to be the preferred material for making fly fishing leaders. It is flexible, strong, and very nearly clear; it's amazing that it's actually natural, it looks so much like plastic. PLEASE NOTE: This page shows the dissection of a silkworm for the gut; if you don't want to see that, please don't read on.
When they are just about ready to spin, having emptied out any undigested food, the worms are dropped into a solution of vinegar and salt. There are various instructions on how salty to make it, but one source says that it's basically as much salt as will dissolve, so that's what I did. The worm floats in the middle of the solution, which is kinda cool looking.
The worm's head is to the right. I've made a small incision in the back, right behind the head. The silk glands practically pop out. They feel soft, slick, and slightly rubbery - like cool hot glue.
I've always heard that the silkworm at the final stage is mostly silk - but it sure makes it dramatically clear when you see the silk glands separated out like this.
Each gland can be gently tugged and pulled out into a single strand, about 18 inches long. I'm not good at it yet, so I broke each strand into two by tugging it wrong. It's strange, how the strand has a pre-set size - you can definitely tell when the strand is stretched and won't stretch any more.
The stretched strands feel a lot like animal sinew. At this stage, they are whitish and opaque.
After drying, the strands clarify. I can see why a lot of the old fly-fishing gut was called "mist colored" - this has a slight blue-gray cast, but is clear like nylon monofilament line. If somebody handed me a strand of it, I would automatically assume it was plastic; they don't feel at all like silk.