The silkworm is the caterpillar or larva form of the silk moth. The larva develops from eggs and then it feeds voraciously on mulberry leaves. When it is full grown, the larva stops feeding and starts spinning a cocoon. The silk fluid is produced from special silk glands which are modified salivary glands. While spinning a cocoon, the worm swings its head from side to side in a series of movements resembling the Arabic numeral eight. The silk fluid on coming into contact with air hardens to form the silk thread. At the same time, a gum like substance, this is known as sericin is produced from it, which cements the threads of silk together.
There is no particular name given to this process but the job of rearing silkworms to obtain silk is called sericulture.
Silk is a natural fiber of exceptional strength, texture, and luster. When silk fibers are spun into thread and woven into fabrics, the result is an exquisite commodity. Silk was first made in China, and for centuries the methods of production were cloaked in secrecy. Eventually, however, the secret and the organisms escaped the control of the Chinese, and thriving silk industries were established in Japan, Arabia, and Spain. Even today, with the vast array of synthetic fibers that rival silk in many ways, the demand for the real thing is still high.Although the larvae of most moths and butterflies produce silk, that produced by Bombyx mori is the silk of commercial importance. As the silkworm prepares to pupate, it spins a protective cocoon. About the size and color of a cotton ball, the cocoon is constructed from one continuous strand of silk, perhaps 1.5 km long. If the silkworm were allowed to mature and break through the cocoon, the silk would be rendered useless for commercial purposes. So the encased insect is plunged into boiling water to kill the inhabitant and dissolve the glue holding the cocoon together. The end of the silk is then located and the cocoon unwound onto a spindle to be made into thread. Life cycle….. .A silkworm starts its life as a tiny egg laid by the female moth. The egg is just about this size: . The egg, lay in the summer or early falls, remains dormant until the warmth of spring stimulates it to start developing. When silkworms first hatch in the spring, they are tiny—3 mm or so—and hairy. They require young tender mulberry leaves during their first few days. As they grow, they can eat tougher leaves, and late in their development they will eat any mulberry leaf you can supply. He larvae advance through five stages of growth, called instars. The silkworm literally outgrows its skin five times, and molts its outgrown skin. With the first molt the silkworm loses its hairy exterior, and for the rest of its larval life its skin is soft and smooth. Silkworms grow rapidly, eventually reaching the size of your ring finger. Then they spin beautiful oval white or yellow cocoons in which they pupate. After 2–3 weeks the creamy-white adult moths emerge from the cocoons. They clamber around, vibrate their wings rapidly, and mate, but they don't fly or attempt to escape from their container. During the adult phase of the life cycle, the silkworm moths do not eat or drink. Males and females look slightly different, and students will be able to tell them apart with a little practice. The female has a larger abdomen. The male has a much larger pair of antennae, which look like long rakes or comb-shaped eyebrows, and vibrates its wings rapidly to attract a female. Silkworm Feeding …..Silkworms eat mulberry leaves; lots of them! But getting leaves in the late fall and winter months are nearly impossible, as the trees are deciduous. There is an alternative food for them called the dry silkworm chow which they cannot prepare. Preparation requires hot tap water and a heat-source such as a microwave oven or stove-top. Water is mixed with the dry powder and then brought to a boil. The resulting mixture is stored in the refrigerator. When firm, the silkworm chow can be sliced and fed to the hungry larvae. The cooked Silkworm Chow can be stored in the refrigerator for a month or two if kept in an airtight container. Make sure your hands are clean when handling the cooked chow as the silkworms are susceptible to bacterial problems if their food is not kept sterile. But remember, if you are raising silkworms in the spring, summer or early fall, fresh leaves are the best food source. If you are using mulberry leaves, the first 10 days the larvae will need catkins or young tender leaves, but after that the larvae will eat any leaf you can provide. Keep leaves in the refrigerator. Feed the silkworms once or twice a day. Obtain silkworm eggs. Eggs of the silkworm must be obtained from a colleague who worked with silkworms last year, or ordered from a biological supply company. If you purchased eggs from a biological supplier, plan to conduct this part as soon as the eggs arrive, because they will hatch 1–2 weeks after you receive them. What to do when they arrive. Purchased silkworm eggs usually arrive loose in a vial. Working on a large piece of white paper, use the little paintbrush to divide the eggs into eight piles, and put one pile into each of eight vials. Cap the vials. Keep them in a warm place out of direct sunlight until you are ready to introduce them to students. Eggs from a colleague may be stuck to paper. If this is the case, cut or tear the paper so that each piece has 10–15 eggs, and put the bits of paper into the vials. Habitat. A shoe box is all that you need to make a silkworm habitat. Choose a place in the room where the silkworms will be warm but not in direct sunlight. Place the shoe box in an open plastic bag, or drape a sheet of plastic over the box. The idea is to reduce evaporation from the leaves a bit without developing a humid environment. If the eggs are scattered all over the box, that is OK, but the larvae should be placed on a leaf. New larvae must be rounded up each day and delivered to a fresh mulberry leaf. Larva. Silkworm larva are delicate at first and should not be handled for the first 2 weeks except with a tiny paintbrush. By the time the larvae are 2 cm (1") long, students can carefully pick up and gently hold them. The larvae seem to survive better if they are kept together in a single culture early in life—later they can be kept in pairs or small groups on students' desks. Plan for spinning. Get a medium-size corrugated cardboard box and a couple of paper egg cartons. Open the egg cartons and attach them to the inside walls of the box. The silkworms will spin in the depressions in the egg cartons. The silkworms must all be in this box for spinning their cocoons. The time for this will be signaled by the first larva that starts to spin, either in your class habitat or, more likely, in one of the group habitats. Prepare for silkworm moths. Once the larvae spin cocoons, they require no further care. The moths will emerge in a couple of weeks and can be handled by students. They do not eat or drink—they mate, lay eggs, and die. Prepare for mating and egg laying. Get a large flat box, or cut a taller one down to about 10 cm (4"). Line the bottom with paper. As the adults emerge, move them to this new box. The moths will stay in the open box. The females will lay eggs on the paper, making them easy to collect. Collect eggs. The eggs will remain viable for a year with minimal care. Seal them in a labeled zip bag and put them in the refrigerator (not the freezer!) as soon as all the moths have died. If you don't refrigerate the eggs, they will still hatch, but over an extended period of time instead of all at once.
The silkworm spins a cocoon after about 1 year. The cocoons are picked and boiled in which the silkworm dies. Then the strand is unraveled and it can be up to 1600m long. It is then reeled and woven. The woven piece of silk is then sold.
The silk worm which hatches from eggs is known as caterpillar. It is a tiny creature, about 6mm long and move about in a looping manner.
The caterpillar stops feeding and returns to corner among the leaves. It now begin to secrete the sticky fluid of its salivary glands through a narrow pore, called spinneret, situated on the hypophyarynx.The sticky substance turns into a fine , long and solid thread of silk into the air. The silk thread is made of 5 filaments stuck together by gummy substance, the secin, which is secreted by two other glands. The thread becomes wrapped around the body of the caterpillar forming a pupal covering or known as cocoon. This process goes on for about 3-4 days at the end of yellow silken cocoon.
Stiffing: For obtaining the commercial silk, the cocoons are treated with hot water or placed in a hot oven to kill the pupae inside; for, if allowed to hatch, they would cut the silk threads while emerging. This process of killing cocoons is called stiffing.
Reeling: The removal of silk thread from cocoons is termed reeling. The silk unwound or reeled off from the cocoons is twisted into thread of commercial silk on a large wheel and transfer to spools. This is called raw silk or reeled silk. The damaged cocoons and waste threads are also teased and spun into threads called spun silk.
Silkworms, offspring of moths, produce their highly-desirable, pricey silk, by spewing out thread from tiny holes in their jaws, which they use to spin into their egg-bearing cocoons. This entire production takes a mere 72 hours, during which time they produce between 500-1200 silken threads. These miniature, mulberry leaf-munching marvels lay, at minimum, 500 eggs each spring, thereby increasing the number of workers for the production line.
The ancient Chinese unearthed the silkworm's secret, and were the first to spin the silkworm's threads into cloth. They kept this covert, top-secret operation, from the rest of the world by imposing the death sentence upon those who smuggled the worm and/or its eggs out of China. Eventually, however, the secret was out, and silkworms are now farmed for their silk, in China, of course, in Japan, in India, in France, in Spain, and in Italy. These countries harness the power of the silkworm through a tedious, labour-intensive, time-consuming process, a process which prominently figures into the price of silk.
Farm workers painstakingly place the 500 plus eggs the prized greyish-white moth lays, upon strips of paper or cloth (not made of silk!), until the following spring, when the incubated eggs hatch, and the tiny, black worms emerge. Once hatched, workers transport the worms to trays brimming with the worm's favorite fodder of finely chopped, white mulberry leaves. After approximately 6 weeks, the satiated worms begin slowly to sway their heads back and forth to signal that show time is at hand.
Once the silkworm completes its cocoon, the farmer snatches his cocoon from him, to prevent the shrunken chrysalis, carefully encased inside, from hatching into a moth in 12 days. The silk farmers ensure that this event does not transpire, and does not kill his moneymaking venture, by exposing the cocoons to heat, thereby executing the chrysalis. Now, the silkworm's labour of love is prepared for the silk production process.
The process begins by bathing the now-empty cocoons in troughs of warm water, which serves to soften the gum binding the silken filaments together. He now proceeds with the arduous task of unravelling several cocoons, and winding the filaments onto a reel that twists 10-12 filaments together into a "single" thread of silk. The end product is a skein of raw silk, which the farmer profits from by selling to the highest bidder.
Cloth and clothing manufacturers, use the trade terminology, in labelling their product, as being either 2 or 3 threaded, depending upon the number of threads woven into the cloth.
