When I was a kid we grew silk worms (larvae of the Bombyx mori moth), feeding them on leaves from the mulberry tree in front of our house. I learned to appreciate the amount of work that goes into silk production. Not only do you have to keep your worms alive until they can spin their silk cocoon (right), but then you have to extract the silk by boiling the cocoons and unwinding the silk filaments.
I found some fun facts about silk, including this one: The fluffy white cocoon spun by a silkworm is one long continuous silk filament that when unwound is usually between 600 and 900 meters long or as long as 1,600 yards.
Silk is another highly renewable resource with less impacts than many fabrics. You have to kill the silk worm when you boil the cocoon, but a single moth that hatches will lay hundreds of eggs. They feed on mulberry leaves, which don't require pesticides or fertilizers to grow.
The negatives are that silk is not a local resource and processing can lead to pollution. Much of the silk available in the U.S. is from China and India. Intensive cultivation practices and chemicals used for cleaning the silk can pollute groundwater. When you add it up, it does take a large amount of resources to produce a small amount of silk--by some estimates, 35 pounds of silk from an acre of mulberry trees.
What to do about it?
I couldn't find any resources on organic certification for silk, although I did find several suppliers selling it. Being organic actually probably doesn't matter as much as for fabrics like cotton, because pesticides aren't really needed. Most people I know don't own a lot of silk, perhaps because the costs of labor and shipping from Asia are built into the price. Personally, I would worry a lot more about the more common fabrics like cotton and synthetics like polyester and rayon.
Also, for those concerned about killing silk worms there are "vegan" silk choices.