Silk Production - The Process of Sericulture

Sericulture is the process of raising silk moths and then harvesting their cocoons in order to obtain silk fiber. Many species of moth spin cocoons that can be used for silk, but the two most common are Bombyx mori, whose cocoons make bombyx silk, and the tussah moth, which produces tussah silk. Bombyx eggs need to hibernate, so the bombyx moth normally produces only one crop of eggs a year (although there is now a chemical process to induce a second hatching). The tussah moth, on the other hand, can produce up to seven "crops" of eggs a year.

Each silk-producing moth eats a different kind of leaf, which explains why silk can have different characteristics. For example, bombyx moths eat leaves from the white mulberry tree, so their cocoons, and therefore their silk, tend to be very light colored-almost white. Tussah moths eat oak leaves, which contain tannin, so their cocoons have more color. Most tussah silk is gold, although it can also be green or tan. But tussah silk for handspinning is also available bleached, which can make look very much like the more expensive bombyx. Tussah, however, does not feel quite the same as bombyx, because it's slightly coarser.

Bombyx moths are raised in the following manner, which is probably not all that different from the raising of other moths (except, of course, for their food):

The eggs are kept in hibernation until the mulberry leaves sprout. Then they're allowed to hatch, and the larvae immediately begin feeding voraciously on the leaves. They shed their skin four times during this stage, eating increasing amounts of leaves as they grow. It has been estimated that the total weight of leaves needed for just 1/10 of an ounce of eggs is about 45 pounds.

After the last shedding the larvae will increase their feeding almost exponentially. It may take up to 180 pounds of leaves for this same amount of eggs-and larvae-to make cocoons which will eventually produce about a pound of usable silk fiber.