It’s spinning time!
The worms have started to convert to spinning. They spend a few hours not eating, then dump out any undigested food, and become spinners. The worm in front has changed over; the one behind has not. They lose quite a bit of length when they make the conversion, because they have downsized their digestive organ systems to make way for the new ones coming in.
The worms will wander about at this stage. Once they find a nice spot (this is in a toilet paper tube, which works great for spinning), they will start laying long loose strands of silk to anchor the cocoon to. This silk is called cocoon strippings, blaze, or keba, and is used in making spun silk. If they are in open trays, the worms can sometimes crawl out and up into inconvenient places, like draperies or the corners of walls.
The worm has now gotten a good start – the cocoon is nearly opaque now, although it will continue to get thicker and more solid. Spinning will continue on the inside for up to three days; after it is completed, the worm will cast off its final caterpillar skin and change to a pupa.
Here, held against a strong backlight, you can see the worm inside still spinning.