Extremely interesting is the history of breeding such an insect as the silkworm. The technology was developed a long time ago, in ancient China. The first mention of this production in Chinese chronicles dates back to 2600 BC, and silkworm cocoons found by archaeologists date back to 2000 BC. e. The Chinese have elevated the production of silk to the status of a state secret, and for many centuries it was the country's obvious priority.
Much later, in the 13th century, Italy, Spain, the countries of North Africa, and in the 16th century Russia began to breed such worms and produce silk fabric. What kind of insect is the silkworm?
The silkworm butterfly and its offspring
The domesticated silkworm butterfly is not found in the wild today and is bred in special factories to obtain a natural thread. An adult is a fairly large light-colored insect, reaching 6 cm in length with a wingspan of up to 5-6 cm. Breeders from many countries are engaged in breeding various breeds of this interesting butterfly. After all, optimal adaptation to the characteristics of various localities is the basis forprofitable production and maximum income. Many breeds of silkworm have been bred. Some give one generation a year, others two, and there are species that give several broods a year.
Despite its size, the silkworm butterfly does not fly, as it has long lost this ability. She lives only 12 days and during this time she does not even eat, having an undeveloped oral cavity. With the onset of the mating season, silkworm breeders deposit pairs in separate bags. After mating, the female for 3-4 days is engaged in laying eggs in the amount of 300-800 pieces per grain, which has an oval shape with significantly varying sizes, which are directly dependent on the breed of the insect. The period of removal of the worm also depends on the species - it can be in the same year, or maybe in the next.
The caterpillar is the next stage of development
The silkworm caterpillar is hatched from eggs at a temperature of 23–25 °C. In the factory, this happens in incubators at a certain humidity and temperature. Eggs develop within 8-10 days, then a brown small up to 3 mm long silkworm larva, pubescent with hairs, appears from the grena. Small caterpillars are placed in special trays and transferred to a well-ventilated warm room. These containers are a structure like a bookcase, consisting of several shelves, covered with a net and having a specific purpose - here the caterpillars constantly eat. They feed exclusively on fresh mulberry leaves, and the proverb “appetite comes with eating”absolutely accurate for determining the voracity of caterpillars. Their need for food grows exponentially, already on the second day they eat twice as much food as on the first.
Moulting
By the fifth day of life, the larva stops, freezes and begins to wait for its first molt. She sleeps for about a day, clasping her legs around a leaf, then, with a sharp straightening, the skin bursts, releasing the caterpillar and giving it the opportunity to rest and again take up satisfying hunger. For the next four days, she devours the leaves with an enviable appetite, until the next molt comes.
Caterpillar transformations
For the entire period of development (about a month), the caterpillar molts four times. The last molt turns it into a rather large individual of a magnificent light pearl shade: the body length reaches 8 cm, the width is up to 1 cm, and the weight is 3-5 g. A large head stands out on the body with two pairs of well-developed jaws, especially the upper ones, called "mandibles". But the most important quality that matters for the production of silk is the presence in an adult caterpillar of a tubercle under the lip, from which a special substance oozes, which hardens on contact with air and turns into a silk thread.
Formation of silk thread
This tubercle ends with two silk glands, which are long tubes with a middle part turned into a kind of reservoir in the body of a caterpillar, accumulating a sticky substance, which subsequently forms a silk thread. If necessary, caterpillar throughthe hole under the lower lip releases a trickle of liquid, which solidifies and turns into a thin, but strong enough thread. The latter plays a big role in the life of an insect and is used, as a rule, as a safety rope, since at the slightest danger it hangs on it like a spider, not being afraid to fall. In an adult caterpillar, silk glands occupy 2/5 of the total body weight.
Steps of building a cocoon
After reaching adulthood after the 4th molt, the caterpillar begins to lose its appetite and gradually stops eating. The silk secreting glands by this time are filled with liquid so that a long thread constantly stretches behind the larva. This means that the caterpillar is ready to pupate. She starts looking for a suitable place and finds it on cocoon rods, timely placed by sericulture along the side walls of the aft "whatnots".
Having settled on a twig, the caterpillar begins to work intensively: it alternately turns its head, applying a tubercle with a hole for the silk gland to different places on the cocoon, thereby forming a very strong network of silk thread. It turns out a kind of frame for future construction. Then the caterpillar crawls to the center of its frame, holding in the air by means of threads, and begins to spin the actual cocoon.
Cocoon and pupation
When building a cocoon, the caterpillar turns its head very quickly, releasing up to 3 cm of thread on each turn. The length of her to create everythingcocoon is from 0.8 to 1.5 km, and the time spent on it takes four or more days. After finishing work, the caterpillar falls asleep in a cocoon, turning into a chrysalis.
The weight of a cocoon with a pupa does not exceed 3-4 g. Silkworm cocoons are very diverse in size (from 1 to 6 cm), shape (round, oval, with bridges) and color (from snow-white to purple). Experts have noticed that male silkworms are more diligent in terms of cocoon weaving. Their pupa dwellings differ in the density of the winding of the thread and its length.
And the butterfly again
After three weeks, a butterfly comes out of the chrysalis, which needs to get out of the cocoon. This is difficult, since it is completely devoid of jaws that adorn the caterpillar. But wise nature solved this problem: the butterfly is equipped with a special gland that produces alkaline saliva, the use of which softens the wall of the cocoon and helps to release the newly formed butterfly. So the silkworm completes the cycle of its own transformations.
However, the industrial breeding of silkworm interrupts the reproduction of butterflies. The bulk of the cocoons is used to produce raw silk. After all, this is a finished product, it remains only to unwind the cocoons on special machines, after killing the pupae and treating the cocoons with steam and water.
So, the silkworm, which will probably never lose its relevance on an industrial scale, is a magnificent example of a domesticated insect,bringing a very considerable income.
