I have been wondering how leaf rollers engineer their nests. How do they bend leaves and build shelters many times bigger than themselves? I finally had a chance to see and to video one in action. I gave this leaf roller a new leaf of its host plant (I think that it is some kind of cherry) and it started spinning and weaving right away.
According to Terrence Fitzgerald, (Caterpillars roll their own. Natural History v. 104 (April 1995) p. 30-7) when the silk comes out of the spinnerets it has the texture of a gel that can be stretched like a rubber band. It soon contracts to its normal size and starts pulling the ends together.
The following pictures show the process, which can be seen better in this video. It worked so fast that the head looks like a blur in some photos. The final image was taken an hour later.
The way you see the fecal pellets work their way down the intestine is pretty interesting too but it doesn't show in this video.

Update, 10/15/2010. This caterpillar pupated and a moth emerged on 10/3/2010. It was badly damaged but there was another cocoon and a moth emerged around 10/13/2010. Here are the pupa (10/3/2010) and adult 10/15/2010):


Higher resolution image