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.
Eriogaster lanestris
Larvae mature through five stages, called instars, over the course of six to seven weeks. During early larval development (instars 1–3), larvae are small and black in coloration, and during late development (instars 4–5), larvae develop urticarial hairs and red coloration. In their fifth instar, larvae lose many of their social behaviors and colonies disband as individuals prepare for pupation.
"E. lanestris" eggs hatch in April and May, and following their emergence, caterpillars immediately construct tents out of silk at their hatching site, or nearby on the same bush. They live in these tents as colonies of approximately 200 of their full siblings during their development. They continually repair and expand the same structure throughout larval development. The tent consists of layers of silk fibers that form air pockets which serve to insulate the nest and provide resting spaces for caterpillars inside. Tent structures are severely damaged by heavy rains, which cause their silk layers to stick together, removing air pockets. Dried silk also becomes brittle and fragile, making it susceptible to breaking and tearing. Additionally, small eggars’ tents are bright white and not well-concealed, so they are easily located and damaged by predators like birds. Maintaining the integrity of the tent is essential to larval colonies’ survival, and they do not abandon the tent until just before pupation.