Silkworm transformation. Silkworm insect. Lifestyle and habitat of the silkworm. Reproduction and life span of the silkworm

The silkworm (lat. Bombyx mori) is a nondescript little butterfly with off-white wings that can't fly at all. But it is thanks to her efforts that women of fashion all over the world have been able to enjoy outfits made of beautiful soft fabrics for more than 5000 years, the brilliance and colorful transfusion of which fascinate at first sight.

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Silk has always been a valuable commodity. The ancient Chinese - the first manufacturers of silk fabric - kept their secret securely. For its disclosure, an immediate and terrible death penalty was due. They domesticated silkworms as early as the 3rd millennium BC, and to this day these small insects work to satisfy the vagaries of modern fashion.

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There are monovoltine, bivoltine and polyvoltine silkworm breeds in the world. The former give only one generation per year, the latter two, and the third several generations per year. An adult butterfly has a wingspan of 40-60 mm, it has an underdeveloped mouth apparatus, so it does not feed throughout its short life. The wings of the silkworm are off-white in color, brownish bandages are clearly visible on them.

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Immediately after mating, the female lays eggs, the number of which varies from 500 to 700 pieces. The laying of a silkworm (like all other representatives of the peacock-eye family) is called grena. It has an elliptical shape, flattened on the sides, with one side slightly larger than the other. On a thin pole there is a recess with a tubercle and a hole in the center, which is necessary for the passage of the seed thread. The size of the grena depends on the breed - in general, Chinese and Japanese silkworms have less grena than European and Persian ones.

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Silkworms (caterpillars) emerge from the egg, to which all the views of silk producers are riveted. They grow in size very quickly, shedding four times in their lifetime. The entire cycle of growth and development lasts from 26 to 32 days, depending on the conditions of detention: temperature, humidity, food quality, etc.

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Silkworms feed on the leaves of the mulberry tree (mulberry), so silk production is possible only in places where it grows. When the time of pupation comes, the caterpillar wraps itself in a cocoon, consisting of a continuous silk thread with a length of three hundred to one and a half thousand meters. Inside the cocoon, the caterpillar transforms into a chrysalis. In this case, the color of the cocoon can be very different: yellowish, greenish, pinkish or some other. True, only silkworms with white cocoons are bred for industrial needs.

flickr/JoseDelgar

Ideally, the butterfly should leave the cocoon on the 15-18th day, however, unfortunately, it is not destined to live up to this time: the cocoon is placed in a special oven and kept for about two to two and a half hours at a temperature of 100 degrees Celsius. Of course, the pupa dies, and the process of unwinding the cocoon is greatly simplified. In China and Korea, fried pupae are eaten, in all other countries they are considered just “production waste”.

flickr/Roger Wasley

Sericulture has long been an important industry in China, Korea, Russia, France, Japan, Brazil, India and Italy. Moreover, about 60% of all silk production falls on India and China.

The history of silkworm breeding

The history of breeding this butterfly, belonging to the family of real silkworms (Bombycidae), is connected with ancient China, a country that for many years kept the secret of making an amazing fabric - silk. In ancient Chinese manuscripts, the silkworm was first mentioned in 2600 BC, and during archaeological excavations in the southwest of Shanxi province, silkworm cocoons dating back to 2000 BC were found. The Chinese knew how to keep their secrets - any attempt to take out butterflies, caterpillars or silkworm eggs was punishable by death.

But all secrets will eventually be revealed. This is what happened with silk production. First, some selfless Chinese princess in the 4th century. AD, having married the king of small Bukhara, she brought him a gift of silkworm eggs, hiding them in her hair. About 200 years later, in 552, two monks came to the emperor of Byzantium, Justinian, who offered to deliver silkworm eggs from distant China for a good reward. Justinian agreed. The monks set out on a perilous journey and returned the same year with silkworm eggs in their hollow staffs. Justinian was fully aware of the importance of his purchase and by a special decree he ordered silkworms to be bred in the eastern regions of the empire. However, sericulture soon fell into decline and only after the Arab conquests flourished again in Asia Minor, and later throughout North Africa, in Spain.

After the IV Crusade (1203–1204), silkworm eggs came from Constantinople to Venice, and since then silkworms have been successfully bred in the Po Valley. In the XIV century. sericulture began in the south of France. And in 1596, silkworms were first bred in Russia - first near Moscow, in the village of Izmailovo, and over time - in the more suitable southern provinces of the empire.

However, even after the Europeans learned to breed silkworms and unwind cocoons, most of the silk continued to be delivered from China. For a long time, this material was worth its weight in gold and was available only to the rich. Only in the 20th century, artificial silk somewhat pressed natural silk on the market, and even then, I think, not for long - after all, the properties of natural silk are truly unique.
Silk fabrics are incredibly durable and last a very long time. Silk is lightweight and retains heat well. Finally, natural silk is very beautiful and lends itself to uniform dyeing.

Used sources.

The silkworm is represented by monovoltine (give one generation a year), bivoltine (give two generations a year) and polyvoltine (give several generations a year) breeds.

Egg

After mating, the female lays eggs (500 to 700 on average), the so-called grena. Grena has an oval (elliptical) shape, flattened laterally, somewhat thicker at one pole; soon after its deposition, one impression appears on both flattened sides. At the thinner pole there is a rather significant depression, in the middle of which there is a tubercle, and in the center of it there is a hole - a micropyle, designed for the passage of the seed thread. The size of grena is about 1 mm long and 0.5 mm wide, but it varies considerably between breeds. In general, breeds of European, Asia Minor, Central Asian and Persian give a larger gren than Chinese and Japanese. Egg laying can last up to three days. Diapause in the silkworm falls on the egg stage. Diapausing eggs develop in the spring of the following year, while non-diapausing eggs develop the same year.

Caterpillar

A caterpillar comes out of the egg (so-called silkworm), which grows rapidly and molts four times. After the caterpillar has gone through four molts, its body becomes slightly yellow. The caterpillar develops within 26-32 days. The duration of development depends on the temperature and humidity of the air, the quantity and quality of food, etc. The caterpillar feeds exclusively on mulberry leaves (mulberry tree). Therefore, the spread of sericulture is associated with the places where this tree grows.

While pupating, the caterpillar weaves a cocoon, the shell of which consists of a continuous silk thread ranging in length from 300-900 meters to 1500 m in the largest cocoons. In the cocoon, the caterpillar turns into a chrysalis. The color of the cocoon can be different: pinkish, greenish, yellow, etc. But for the needs of industry, only silkworm breeds with white cocoons are currently bred.

The release of butterflies from cocoons usually occurs on the 15-18th day after pupation. But the silkworm is not allowed to survive to this stage - the cocoons are kept for 2-2.5 hours at a temperature of about 100 ° C, which kills the pupa and simplifies the unwinding of the cocoon.

A sticky substance is released from a small tubercle under the lower lip of the caterpillar, which, upon contact with air, immediately solidifies and turns into a silk thread. The thread is very thin, but can withstand weight up to 15 grams.

All modern domestic animals and cultivated plants are descended from wild species. Not without an insect on the farm - silkworm butterflies. Over four and a half millennia of breeding work, it was possible to breed breeds that give silk of different colors, and the length of a continuous thread from one cocoon can reach a kilometer! The butterfly has changed so much that it is now difficult to say who was its wild ancestor. In nature, the silkworm is not found - without human care, it dies.

Recall that many other caterpillars weave a cocoon of silky threads, but only in the silkworm they have the properties we need. Silk threads are used to produce fabrics that are very durable and beautiful; they are used in medicine - for sewing up wounds and cleaning teeth; in cosmetology - for the manufacture of decorative cosmetics, such as shadows. Despite the advent of artificial materials, natural silk threads are still widely used.

Who first came up with the idea of ​​weaving silk fabric? According to legend, four thousand years ago, a silkworm cocoon fell into a cup of hot tea, which the Chinese empress drank in her garden. Trying to pull it out, the woman pulled on a protruding silk thread. The cocoon began to unwind, but the thread did not end. It was then that the quick-witted empress realized that yarn could be made from such fibers. The Chinese emperor approved the idea of ​​his wife and ordered his subjects to grow mulberry (white mulberry) and breed silkworm caterpillars on it. And to this day, silk in China is called the name of this ruler, and her grateful descendants elevated her to the rank of a deity.

It took a lot of work to get beautiful silk from butterfly cocoons. To begin with, the cocoons need to be collected, discarded and, most importantly, unwound, for which they were dipped into boiling water. Next, the thread was strengthened with sericin - silk glue, which was then removed with boiling water or hot soapy water.

Before dyeing, the thread was boiled and bleached. They painted it with vegetable pigments (gardenia fruits, moraine roots, oak acorns), or mineral pigments (cinnabar, ocher, malachite, white lead). And only then they wove yarn - by hand or on a loom.

As early as one and a half thousand years BC, clothes made of silk fabrics were common in China. In other Asian countries and among the ancient Romans, silk appeared only in the 3rd century BC - and then it was fabulously expensive. But the manufacturing technology of this amazing fabric remained a secret for the whole world for many centuries, because an attempt to take the silkworm out of the Chinese empire was punishable by death. The nature of silk seemed mysterious and magical to Europeans. Some believed that silk was produced by giant beetles, others believed that in China the earth was soft, like wool, and therefore, after watering, it could be used to produce silk fabrics.

The secret of silk was discovered in the 4th century AD, when a Chinese princess presented a gift to her fiancé, the king of Lesser Bukhara. These were silkworm eggs, which the bride secretly took out of her homeland, hiding in her hair. Around the same time, the secret of silk became known to the Japanese emperor, but here sericulture for some time was the monopoly of the imperial palace alone. Then silk production was mastered in India. And from there, with two monks who placed silkworm eggs in the hollow handles of their staffs, they ended up in Byzantium. In the 12th-14th centuries, sericulture flourished in Asia Minor, Spain, Italy and France, and in the 16th century it appeared in the southern provinces of Russia.

Silkworm pupa

However, even after the Europeans learned to breed silkworms, most of the silk continued to be delivered from China. Along the Great Silk Road - a network of roads running from east to west - it was taken to all countries of the world. Silk outfits remained a luxury item, silk also served as an exchange currency.

How does a small white butterfly live - "silk queen"? Its wingspan is 40-60 millimeters, but as a result of many years of cultivation, butterflies have lost the ability to fly. The mouth apparatus is not developed because the adult does not feed. Only the larvae differ in an enviable appetite. They are fed with mulberry leaves. When feeding on other plants that the caterpillars "agree" to eat, the quality of the fiber deteriorates. On the territory of our country, representatives of the family of true silkworms, to which the silkworm belongs, are found in nature only in the Far East.

Silkworm caterpillars hatch from eggs, the laying of which is covered with a dense shell and is called grena. In sericulture farms, grena is placed in special incubators, where the necessary temperature and humidity are maintained. After a few days, small, three-millimeter dark brown larvae appear, covered with tufts of long hair.

Hatched caterpillars are transferred to a special aft shelf with fresh mulberry leaves. After several molts, the babies grow up to eight centimeters, and their bodies become white and almost naked.

The caterpillar, ready for pupation, ceases to feed, and then wood rods are placed next to it, to which it immediately passes. Holding on to one of the rods with its abdominal legs, the caterpillar throws its head to the right, then back, then to the left and applies its lower lip with a "silk" tubercle to various places on the rod.

Caterpillars are fed with mulberry leaves.

Soon a rather dense network of silk thread is formed around it. But this is only the basis of the future cocoon. Then the "craftswoman" crawls to the center of the frame and begins to curl the thread: releasing it, the caterpillar quickly turns its head. The tireless weaver works on the cocoon for about four days! And then it freezes in its silk cradle and turns into a chrysalis there. After about 20 days, a butterfly emerges from the chrysalis. She softens the cocoon with her alkaline saliva and, helping herself with her legs, hardly gets out to start looking for a partner for procreation. After mating, the female lays 300-600 eggs.

However, not every caterpillar is given the opportunity to turn into a butterfly. Most of the cocoons are sent to the factory for raw silk. One centner of such cocoons yields approximately nine kilograms of silk thread.

It is interesting that the caterpillars, from which males are later obtained, are more diligent workers, their cocoons are denser, which means that the thread in them is longer. Scientists have learned to regulate the sex of butterflies, increasing the yield of silk during its industrial production.

Such is the story of the small white butterfly that made ancient China famous and made the whole world worship its magnificent product.

Olga Timokhova, Candidate of Biological Sciences

The silkworm is a very interesting insect that has long been known to man as source of silk. According to some data mentioned in Chinese chronicles, the insect became known as early as 2600 BC. The process of obtaining silk for centuries in China was a state secret, and silk became one of the clear trade advantages.

Starting from the 13th century, other countries, including Spain, Italy, and North African countries, mastered the technology of silk production. In the 16th century, technology reached Russia.

Now the silkworm is actively bred in many countries, and in Korea and China it is used not only to obtain silk, but also for food. Exotic dishes that are prepared from it are distinguished by originality, and silkworm larvae are used for the needs of traditional medicine.

India and China are leaders in the production of silk, and it is in these countries that the number of silkworms is the largest.

What does a silkworm look like

This insect earned its unusual name thanks to the tree that it feeds on. Mulberry - a tree, which is also called mulberry, is the only source of food for the silkworm.

silkworm caterpillar eats a tree day and night, which can even lead to its death if the caterpillars occupy such trees on the farm. For the production of silk on an industrial scale, these trees are grown specifically for feeding insects.

The silkworm goes through the following life cycles:

The silkworm butterfly is a large insect, and its wingspan reaches 6 centimeters. It has a white color with black spots, on the wings, in front of them, there are notches. Pronounced comb mustache distinguish males from females, in which such an effect is almost imperceptible.

The butterfly has practically lost the ability to fly, and modern individuals spend their entire lives without rising into the sky. This led to their very long content in unnatural living conditions. Moreover, according to available facts, insects stop eating after turning into butterflies.

The silkworm acquired such strange features due to keeping it at home for many centuries. This has led to now the insect cannot survive without human care.

The silkworm over the years of its breeding has managed to be reborn into two main species: monovoltine and polyvoltine. The first species lays larvae once a year, and the second - up to several times a year.

Hybrid silkworm individuals can have many differences in terms of such traits as:

• body shape;
• wing color;
• dimensions and general shape of the butterfly;
• pupa dimensions;
• color and shape of caterpillars.

The larvae or eggs of this butterfly in the scientific community are called Grena. They have an oval shape flattened laterally, with elastic transparent film. The dimensions of one egg are so small that for one gram of weight their number can reach two thousand pieces.

Immediately after the butterfly lays eggs, they have a light milky color or yellowish color. As time passes, changes occur, leading to the appearance of a pink hue in the larvae, and then to a complete change in color to purple. If the color of the eggs does not change over time, then the larvae have died.

Silkworm eggs have a fairly long maturation period. He lays them in the summer months: in July and August, and then they hibernate until spring. The processes taking place in them at this time slow down significantly in order to survive the impact of low winter temperatures.

If grena hibernates at temperatures not lower than +15 degrees, then there is a risk of poor development in future caterpillars, so in winter you need provide for grena optimum temperature. Caterpillars appear before the leaves have time to grow on the trees, so grena is stored in refrigeration units at a temperature of 0 to -2 degrees throughout this period.

The caterpillars of this butterfly are also called silkworms, which cannot be considered a scientific name. Externally, silkworm caterpillars look like this:

Immediately after birth, the caterpillar has a very small size and weight, not exceeding half a milligram. Despite such dimensions, all biological processes in the caterpillar proceed normally, and it begins to actively develop and grow.

The caterpillar has very developed jaws, pharynx and esophagus, so that all food consumed is very quickly and well absorbed. Each such small caterpillar has over 8,000 muscles, which allows it to bend in intricate poses.

In forty days, the caterpillar grows to more than thirty times its original dimensions. During the growth period, she sheds her skin, which for natural reasons becomes small for her. This is called a molt.

During molting, the silkworm caterpillar stops eating tree leaves and finds a separate place for itself, usually under the leaves, where, firmly attaching to them with legs, it freezes for some period. This period is also called the sleep of the caterpillar.

With the advent of time, the head of the renewed caterpillar begins to break through from the old skin, then it comes out all in its entirety. At this time, you can not touch them. This can lead to the fact that the caterpillar simply does not have time to throw off the old skin and die. A caterpillar molts four times in its life.

An intermediate stage in the transformation of a caterpillar into a butterfly is a cocoon. Caterpillar creates a cocoon around itself and inside it turns into a butterfly. These cocoons are of the greatest interest to humans.

The moment when a butterfly should be born and leave its cocoon is very easy to determine - it starts to move literally a day before, and you can hear light tapping inside. This knock appears because at this time the already mature butterfly is trying to free itself from the skin of the caterpillar. It is curious that the time of the appearance of the silkworm butterfly into the world is always the same - from five to six in the morning.

A special glue-like liquid secreted by butterflies helps them break free from the cocoon.

The life of a moth is limited to only twenty days, and sometimes they do not even live up to 18 days. At the same time, it is possible meet among them centenarians who live for 25 and even 30 days.

Due to the fact that the jaws and mouth of butterflies do not have sufficient development, they cannot eat. The main task of the butterfly is to continue the genus, and in their short life they manage to lay many eggs. In one laying, the female silkworm can lay up to a thousand of them.

It is noteworthy that even if the insect loses its head, egg laying process will not be interrupted. The body of a butterfly has several nervous systems, which allows it to continue laying and live for a long time, even in the absence of such a significant part of the body as the head.