Silk
Silk moths lay eggs on specially prepared paper. The eggs hatch and the caterpillars (silkworms) are fed fresh mulberry leaves. After about 35 days and 4 moltings, the caterpillars are 10,000 times heavier than when hatched and are ready to begin spinning a cocoon. A straw frame is placed over the tray of caterpillars, and each caterpillar begins spinning a cocoon by moving its head in a pattern. Two glands produce liquid silk and force it through openings in the head called spinnerets. Liquid silk is coated in sericin, a water-soluble protective gum, and solidifies on contact with the air. Within 2–3 days, the caterpillar spins about 1 mile of filament and is completely encased in a cocoon. The silk farmers then heat the cocoons to kill them, leaving some to metamorphose into moths to breed the next generation of caterpillars. Harvested cocoons are then soaked in boiling water to soften the sericin holding the silk fibers together in a cocoon shape. The fibers are then unwound to produce a continuous thread. Since a single thread is too fine and fragile for commercial use, anywhere from three to ten strands are spun together to form a single thread of silk.
Macropis nuda
After the larval feeding period, pupae spin the cocoons in which they will hibernate until the next spring. Cocoons completely occupy the cells, and strongly adhere to the sides of the cell, but not the closure. There is a small hole near the apex of the cocoon, opening to the soil closure of the cell. This allows exchange of oxygen and carbon dioxide as the waxy oil coating the cell and the silk of the cocoon does not allow for gas movement. Not only does the cocoon allow safety from the cold of the winter, it may also serve as a barricade to protect against parasites and predators.