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.
Orbiculariae
Whether spiders that weave true orb webs form a coherent group, and so should be classified together, is a question that has a long history. Two groups of spiders that spin orb webs are the Uloboridae and the Araneidae. Although their webs have a very similar overall architecture, the sticky catching threads are created in different ways. Uloborid spiders have a cribellum – a flat plate from which a particular kind of silk emerges – and a calamistrum – a structure formed of bristles on the metatarsus of the fourth leg, used to "comb" the cribellate silk into extremely fine strands that are adhesive without having any "glue" present. Araneid spiders have silk-producing organs that add fine droplets of a glue-like substance to silk of normal thickness to create viscid silk. (Spiders that do not spin orb webs can also be divided into those that produce cribellate silk and those that produce viscid silk.)