The fashion industry of the whole world, and any person who prefers clothes made from natural fabrics, undoubtedly, are connoisseurs and active consumers of a unique natural product – natural silk. If it were not for the silkworm, we would not know what silk is. It is impossible to imagine something smoother and more pleasant to the touch and surprisingly comfortable to wear as a ready-made piece of clothing.
Origin of the species and description
Photo: Silkworm
It is believed that the production of silk with the help of silkworms existed as early as the Yangshao period (about 5000 BC). Despite the fact that a huge amount of time has passed since then, the basic elements of the production process have not changed to this day. In the international classification, the silkworm is called Bombyx mori (Latin), which literally means “silk death.”
Video: Silkworm
This name is not accidental. It arose because the main task in the production of silk is to prevent butterflies from flying out of the cocoon in order to prevent damage to the silk thread entangling it. For this purpose, the pupae are killed inside the cocoons by heating them to high temperatures.
Interesting fact: Dead pupae left after unwinding the silk thread are a rather valuable product in terms of their nutritional properties, used food.
The silkworm is a butterfly from the True silkworm family. Despite the presence of wings with a span of 40-60 mm, for a long time the development of mulberry production, she almost forgot how to fly. Females do not fly at all, and males make short flights during the mating season.
The name eloquently indicates the habitat of these insects – mulberry trees, or mulberry, as they are commonly called in our country. Dark, sweet and juicy fruits of mulberries, similar to blackberries, are to many tastes, but it is the leaves of these trees that are used as food for silkworms. The larvae eat them in huge quantities, and do it around the clock, without interrupting even at night. Being nearby, you can hear a rather loud characteristic sound of this process.
While pupating, the silkworm caterpillars begin to weave a cocoon consisting of a continuous finest silk thread. It can be white, or it can have various shades – pink, yellow and even greenish. But in modern silk production, it is white cocoons that are considered valuable, so only breeds that produce white silk thread are used in breeding.
Interesting fact: Since natural silk thread is a protein product, it can dissolve under the influence of aggressive chemical detergents. This fact must be taken into account when caring for products made of natural silk.
Appearance and features
Photo: Butterfly silkworm
Outwardly, the silkworm is rather plain, an adult looks like an ordinary moth or a large moth. It has large wings of a gray or off-white color with clearly “traced” dark streaks. The body of the silkworm is quite massive, completely covered with a dense layer of light hairs and visually divided into transverse segments. On the head there is a pair of long antennae, similar to two combs.
If we talk about the life cycle of the silkworm, it is necessary to distinguish between wild insects and domesticated breeds. In captivity, the silkworm does not survive to the stage of butterfly formation and dies in a cocoon.
Its wild counterparts manage to live through all four stages characteristic of insects of any kind:
- egg;
- caterpillar (silkworm);
- chrysalis;
- butterfly.
The larva emerging from the egg is very small, only about three millimeters long. But as soon as she begins to eat the leaves of the mulberry tree, doing this continuously day and night, she gradually increases in size. In a few days of its life, the larva manages to survive four molts and eventually turns into a very beautiful pearl-colored caterpillar. Its body is about 8 cm long, about 1 cm thick, and an adult weighs about 3-5 g. The head of the caterpillar is large, with two pairs of well-developed jaws. But its main feature is the presence of special glands ending in a hole in the oral cavity, from which it releases a special liquid.
Interesting fact: Due to the exceptional strength of natural silk thread, it is used in the production of bulletproof vests.
Upon contact with air, this liquid hardens and turns into the very famous and unique silk thread, which is so valued in silk production. For silkworm caterpillars, this thread serves as material for building cocoons. Cocoons come in completely different sizes – from 1 to 6 cm, and various shapes – round, oval, with bridges. The color of cocoons is most often white, but it can have color shades – from yellowish-golden to lilac.
Now you know what a butterfly and a silkworm caterpillar look like. Let's see where the silkworm lives.
Where the silkworm lives
Photo: Silkworm in Russia
It is believed that China is the birthplace of the modern silkworm. Already in the period of 3000 BC. its mulberry groves were inhabited by a wild species of insect. Subsequently, its active domestication and distribution throughout the world began. In the northern regions of China and in the south of the Primorsky Territory of Russia, wild silkworm breeds still live, from which, presumably, the species began to spread throughout the world.
The habitat of the silkworm today is due to the development of the mulberry production. For the purpose of its distribution, insects are brought to many areas with a suitable climate. So, at the end of the 3rd century AD. silkworm colonies inhabited India, and a little later they moved to Europe and the Mediterranean.
For a comfortable stay and the production of silk thread, the silkworm needs certain climatic conditions, without which the insect does not perform the main function consumed by silkworms – it does not form cocoons and does not pupate. Therefore, its habitats are areas with a warm and moderately humid climate, without sudden changes in temperature, with an abundance of vegetation, and in particular, mulberry trees, the leaves of which are the main food of the silkworm.
China and India are considered the main habitat of the silkworm. They produce 60% of the world's silk. But due to the fact that sericulture has become one of the important industries in the economy of many other countries, today silkworm colonies inhabit areas of Korea, Japan, Brazil, and in the European part they are distributed in certain regions of Russia, France and Italy.
What does the silkworm eat?
Photo: Silkworm cocoons
About the basic diet nutrition of the silkworm as well as possible says its name. It feeds exclusively on the leaves of the mulberry tree, which is also called mulberry or mulberry. Seventeen varieties of this plant are known, which are distributed exclusively in warm climates – the subtropical zones of Eurasia, Africa and North America.
The plant is quite capricious, grows only in comfortable conditions. All its species are fruit-bearing, have tasty juicy fruits that look like blackberries or wild raspberries. The fruits vary in color – white, red and black. Black and red fruits have the best aroma, they are widely used in cooking for making desserts and pastries, and they are also used to make wine, mulberry vodka and soft drinks.
For the purposes of mulberry production, white and black mulberries are widely cultivated. But the fruits of these trees are not of interest to the silkworm, it feeds exclusively on fresh mulberry leaves. Under natural conditions, mulberry groves are densely populated by this insect. Silk growers who want to get a lot of silk cocoons take care of the plantations of this plant, take care of them, creating comfortable conditions for growth – a sufficient amount of moisture and protection from the scorching sun.
On mulberry farms, silkworm larvae continuously supply fresh portions of crushed mulberry leaves. They eat constantly, day and night. In the room where pallets with colonies of larvae are located, there is a characteristic rumble from working jaws and the crunch of mulberry leaves. From these leaves, silkworms get all the necessary substances for the reproduction of a valuable silk thread.
Peculiarities of character and lifestyle
Photo: Silkworm caterpillar
The centuries-old development of silk production has left its mark on the way of life of the silkworm. It is assumed that wild individuals at the dawn of their appearance were perfectly able to fly, as evidenced by the presence of fairly large wings in this insect species, which are quite capable of lifting the silkworm's body into the air and moving it to a considerable distance.
However, under conditions of domestication, insects have practically forgotten how to fly. This is due to the fact that most individuals do not survive to the butterfly stage at all. Silk breeders kill the larvae immediately after the formation of the cocoon, so that the butterfly leaving it does not damage the precious silk thread. In nature, silkworm butterflies are quite viable, but evolutionary changes have also affected them. Males are a little more active, and make short flights during the mating season.
Fun fact: Female silkworms can live their entire short lives – about 12 days – without making a single beat of their wings.
There is evidence that mature silkworms do not eat at all. Unlike the previous form of their life cycle – the caterpillar, which has powerful jaws and absorbs food continuously – butterflies have an underdeveloped mouth apparatus and are unable to grind even the lightest food.
For a long time of domestication, insects have become completely “lazy”, it has become difficult for them to survive without human care and guardianship. Silkworms do not even try to find food on their own, waiting to be fed ready-to-eat, finely chopped mulberry leaves. In nature, the caterpillars are more active, it is even known that with a lack of habitual food, they sometimes feed on the foliage of other plants. However, the silk thread produced from this mixed diet is thicker and coarser, and is not of sufficient value in silk production.
Social Structure and Reproduction
Photo: Silkworm
The silkworm is a paired insect that reproduces and has the same life cycle as most butterflies. Currently, many of its species have been bred. Some give birth only once a year, others – twice, but there are those that are able to lay eggs several times a year.
During the mating period, males become more active and even make short flights, which is unusual for them at normal times. In nature, one male can fertilize several females. On artificial farms, with the onset of the mating season, silkworm breeders plant paired insects in separate bags and wait 3-4 days after mating until the female lays eggs. In a silkworm clutch, on average, from 300 to 800 eggs. Their number and size depend on the breed of the insect, as well as the period of caterpillar breeding. There are more productive types of silkworm, which are most in demand among silkworm growers.
In order for a worm to hatch from an egg, the ambient temperature is about 23-25 degrees and its moderate humidity. In mulberry production, these conditions are created artificially by employees of incubators, while in nature, laid eggs are forced to wait for favorable conditions for several days. Silkworm eggs hatch into tiny larvae (or silkworms) about 3 mm in size, having a brown or yellowish color. From the moment of their birth, the larvae begin to eat, and their appetite grows every day. After a day, they are able to eat twice as much food as the day before. It is not surprising that with such a plentiful diet, the larvae quickly grow into caterpillars.
On the fifth day of life, the larva finally stops eating and freezes without movement, so that the next morning, straightening up with a sharp movement, shed its first skin. Then she starts eating again, devouring it with great relish for the next four days, until the next cycle of molting. This process is repeated four times. As a result, the silkworm larva turns into a very beautiful caterpillar with a pearl-colored skin. By the end of the molting process, she has already formed an apparatus for the production of silk thread. The caterpillar is ready for the next step – spinning a silk cocoon.
By this time, she loses her appetite and gradually refuses to eat at all. Its silk-secreting glands are overflowing with liquid, which is secreted outside and everywhere stretches behind the caterpillar with a thin thread. The caterpillar begins the process of pupation. She finds a small twig, weaves a future frame for a cocoon on it, crawls into its center and begins to twist the thread around herself, actively working with her head.
The pupation process lasts an average of four days. During this time, the caterpillar manages to use from 800 m to 1.5 km of silk thread. Having completed the formation of a cocoon, the caterpillar falls asleep inside it and turns into a chrysalis. Three weeks later, the chrysalis becomes a butterfly and is ready to emerge from the cocoon. But the silkworm butterfly has too weak jaws to gnaw a hole in the cocoon to get out. Therefore, a special liquid is released in her oral cavity, which, wetting the walls of the cocoon, corrodes them, making way for the butterfly to exit.
At the same time, the continuity of the silk thread is disrupted and the unwinding of cocoons after a flying butterfly turns into a laborious and inefficient process. Therefore, on mulberry farms, the life cycle of the silkworm is interrupted at the stage of pupation. Most of the cocoons are exposed to high temperatures (about 100 degrees), at which the larva inside dies. But the cocoon, consisting of the thinnest silk thread, remains intact.
Silk breeders leave a certain number of individuals alive for the purpose of their further reproduction. And the dead larvae left after the unwinding of cocoons are willingly eaten by the inhabitants of China and Korea. The natural life cycle of the silkworm ends with the appearance of a butterfly, which, a few days after leaving the cocoon, is ready to reproduce.
Natural enemies of the silkworm
Photo: Silkworm butterflies
In the wild The enemies of the silkworm are the same as those of other insect species:
- birds;
- insectivorous animals;
- parasitic insects;
- pathogens.
As for birds and insectivores, the picture is clear with them – they eat both caterpillars and adult silkworm butterflies. The rather large size of both is an attractive prey.
But there are certain types of silkworm natural enemies that are more sophisticated and cause much more harm to its populations. Among parasitic insects, the most dangerous for silkworms are blackflies or tahini (family Tachinidae). The female barberry lays her eggs on the body or inside the silkworm, and parasite larvae develop in its body, eventually leading to the death of the insect. If the infected silkworm manages to survive, it reproduces the infected offspring.
Another deadly threat to the silkworm is pebrin disease, which is caused by a pathogen that has the scientific name Nosema bombycis. The disease is transmitted from an infected adult to its larvae and leads to their death. Perbina is a real threat to silk production. But modern silkworm breeders have learned to effectively deal with its pathogen, as well as with parasitic insects that are dangerous for cultivated individuals.
Interesting fact: In its natural environment, the silkworm is forced to confront enemies on its own. Parasite-infested caterpillars have been known to begin eating plants containing toxic alkaloids. These substances have a detrimental effect on the larvae of parasites, giving the infected caterpillar a chance to survive.
Population and species status
Photo: Silkworm Cocoons
The distribution of the silkworm in the natural environment, as well as the comfort of its habitat, are entirely due to the presence of a fodder plant – the mulberry tree. In the main areas of its growth – in China and Japan, in Europe and India – insect populations are quite numerous.
In an effort to obtain the main product of the production of silkworms – natural silk – people try to maintain favorable conditions for the life of an insect. Protected areas and reserves are being created, the number of mulberry plantations is constantly replenished, and proper care of plants is provided.
A comfortable temperature and humidity are maintained on silk farms, which are necessary for the full development of the silkworm and the production of high-quality silk raw materials. Man provides insects with continuous nutrition in the form of mulberry leaves, protects them from diseases and parasites, thereby preventing a significant decrease in numbers.
Scientists are constantly working on breeding new breeds of silkworms, the most viable and productive. Given such human care, it is not surprising that the populations of a domesticated insect are much more numerous than those living in the wild. But this does not at all indicate the threat of extinction of the species. It's just that the silkworm has moved from its natural habitat to human care. Silkworm breeders are more concerned about the status of the insect population. And, despite the mass killing of silkworm pupae in artificial conditions, the number of individuals is regularly restored and even increased.
The silk thread produced by the silkworm has unique properties. It is thinner than a human hair by almost eight times and is very durable. The length of such a thread in one cocoon of an insect can reach one and a half kilometers, and the fabrics obtained on its basis are surprisingly delicate to the touch, beautiful and comfortable to wear. Due to this fact, the silkworm is of great importance for silk producers in many countries, bringing them considerable income.
