Silk: Caterpillars: The Pulse of the Planet daily radio program offers free legal online mp3 downloads, exploring the world of sound in nature, culture and science, with audio adventures, world music, extraordinary sound portraits, science diaries, and nature ring-tones; an amazing sonic experience.

Airdate: Nov 23, 2005
Scientist: Professor Michael Wells (see home address in details)

Silk: Caterpillars

Silk: Caterpillars
A little caterpillar + a big appetite and a lot of help = the world's finest fabric.


ambience: Silkworms munching mulberry leaves

We're listening to the sounds of caterpillars munching mulberry leaves -- not just any caterpillars, mind you. If you're wearing a silk shirt or blouse, it could have had its origins right here. I'm Jim Metzner, and this is the Pulse of the Planet. The only way to manufacture silk is to harvest silkworms, feed them and encourage them to spin cocoons from which silk thread is made. The process originated in China thousands of years ago.

"The one thing to realize about silkworms is that they have been breed specifically to make silk."

Dr. Michael Wells is a biochemist at the University of Arizona.

"So these insects actually can't fly. So they tend to put them just in big plastic barrels and let them mate, and lay them on pieces of paper. And then these are put into trays with freshly harvested mulberry leaves. The labor intensive part is that about every 6 to 8 hours they have to replace them with a fresh batch of mulberry leaves."

A silkworm grows from about the size of a pinhead to over 3" in length. Along the way it chews a prodigious amount of mulberry leaves, increasing its body mass about 10,000 times from its original mass.

"So you need a large number of mulberry trees, and a lot of people going out and picking leaves and chopping them up. And it takes about 3 to 4 weeks to grow from eggs to the stage where they spin the cocoons. They are put in, now, into plastic devices that look kind of like egg crates where they spin their cocoons - that keeps them all in one place, and then it makes it easy to harvest the cocoons. And then the cocoons are simply put into big vats of an alkaline solution - silk threads are drawn out from that vat with big machines."

Pulse of the Planet is presented by DuPont, bringing you the miracles of science, with additional support provided by the National Science Foundation.