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.
Hemipepsis ustulata
The well-nourished grub begins to spin a delicate framework to support its cocoon.
The "Hemipepsis" cocoon is a brown, silk structure. It is slightly wider at the end from which the wasp will emerge. The inner wall is varnished, but no inner cocoon is seen. Completion takes several hours, and at the end of it, the grub evacuates its alimentary canal; this meconium, or first stool, becomes a hardened mass at the end of the cocoon. The grub is much smaller than it was at the end of feeding because it has expended so much body content on spinning the cocoon and voiding its alimentary canal. The cocoon turns a greasy amber yellow from the original silky gray. The time of hatching is dependent on the season. A cocoon formed early in the summer may hatch the same summer, but a late summer or autumn brood may remain in cocoon form until the following spring or summer. Once the grub reaches the pupal stage, the grub lies extended and quiet. The head capsule splits along the midline, and a glassy, whitish pupa forces its way out of the discarded, shriveling larval skin. The pupa turns creamy yellow, with gray-blue, large compound eyes showing through the thin integument. One can also see the antenna, stubby wing pads, and back spines.