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.
Chrysiridia rhipheus
After completing all but its last moult, the caterpillar spins a cocoon out of silk. The cocoon can be in the tree crown or between two leaves, but is most often near the ground, between moss and bark. It is an open network cocoon with large and irregular mesh. In the warm season, the cocoon takes about 10 hours to spin, the metamorphosis takes place about 29 hours later and lasts about 6 minutes. These durations are slightly longer in the cold season. The chrysalis stage lasts 17 days in November, the warmest month, and 23 days in July, the coldest month. Five to six days before eclosion, the motifs of the wings start to become visible. The moth emerges during the night or in low light, by splitting the pupal case from the top. Once out of the pupal exuvia (the pupal exoskeleton), the moth finds a horizontal surface, from which it suspends itself by its four anterior legs. The wings are deployed in about 10 minutes, by pumping haemolymph into the wing veins. The moth then beats them a few times, waits 45 minutes to let them harden, then beats them lightly again. The moth finally takes flight between one-and-a-half and two hours later.