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BOMBYX MORI, the silkworm

 

Among the caterpillars, which can produce the silk, the species Bombyx mori or silkworm of the mulberry tree, is the one that gives the most beautiful and the most estimated products.
The silkworm is native of the Southern part of China, where it seems to be bred, 2700 years before our era. The eggs, called seeds, were imported successively in India, in Persia and in the various parts of Asia, it was in the VI-th century of our era that they were introduced in Constantinople where the emperor Justinien made an object of public utility of it.

Further the breeding arrived in Greece, in Arabia, in Spain, in Italy, then in France, at about XIII-th century. Lyons began by 1450 to produce silk trades, Tours was the second city of France which was engaged in this kind of manufacture in 1470. In the reign of Henri IV the culture of the mulberry tree extended considerably in the south and the centre of France.

The caterpillar of the silkworm distinguishes itself especially from the other bombyx by a sort of horn on the last segment, in a similar way of sphinx, although it does not belong to this family. Arrived at its complete development, the silkworm is consisted of a head or a snout and of a body. The head is consisted of a jaw armed with teeth, below the lower lip is the trunk by where goes out the silk supplied by two silky glands, there are six eyes of every side of the head.

The body, hairless, whitish, with black spots, according to species, is divided into 12 joints with 3 pairs of hard skin paws and 5 pairs of soft, flexible membraneous paws, they are flat, provided with small hooks and fix the worms on the objects by acting as suckers.
The silkworm, as well as the insects of this type, passes during its life by three successive alterations. Larva at first, it forms in the last days of its life an silky envelope called cocoon in which it retreats into to become chrysalis and where from it goes out a short time later in the state of butterfly.

The other species of caterpillars give also the silk under the shape of a cocoon, of which Anthéroea Yama-Maî and Anthéroea Pernyï, which feed on oak leaves. Worms live outdoors in a wild state and supply a cocoon about 3 times bigger than the Bombyx mori, these cocoons give a silk called Tussah often used as weft in soft furnishing fabrics and in certain material of clothing. The breeding of the silkworms starts in spring, that is in the first push of the mulberry trees leaves, in special constructions called "magnaneries", from the Provençal word magnan which means: silkworm.

Breeding includes two distinct periods since the state of seeds until that of the cocoon.
These two periods are the incubation of the seed and the breeding strictly speaking of the worm.

 

First period: Incubation of the seed.

This period lasts about 11 days during which it is necessary to vary the temperature of the steam room from 17 °C until 28 °C gradually.

In the 5-th day eggs become pale, the worm is already formed, and with a magnifying glass we can distinguish the insect through the shell which contains it.

In 7-th and 8-th day some births take place, it is that it called the precursors.

During the last three days, hatching is plentiful, it is necessary then to make frequent withdrawing by means of small nets in tulle that we place on the worms, we spread on these nets leaves of mulberry shop finely and immediately the young worms smelling their food pass through meshes.

After about half-hour we removes the net which bring a rack prepared in advance, then we proceeds to another withdrawing.

After the birth of the 11-th day we can throw away the not hatched eggs, as well as moreover the precursors to not multiply series.

An ounce of 30 grams seeds give about from 40 to 50.000 worms which produce from 30 to 40 kg of fresh cocoons.

 

Second period: Breeding of worms.

The second period which lasts approximately from 30 to 40 days is subdivided into five ages including for each one the time which passes from a skin to the other one, or from a sleep to the other one; these crises consist of a change of skin called slough. Each one will understand the necessity of these sloughs knowing that the worm as it is going to spin its cocoon is 40 times as big as in the birth, it is so impossible for the first skin to have enough elasticity to reach to contain such a volume. The far-sighted nature has stretched on the caterpillar body the embryos of the skin of every slough.

The animal growing more than the skin can distend, this one and is replaced by a second able to contain the new volume of the worm until the following slough. The worm, during these crises raises its head, is completely motionless and refuses any food, what says to certain breeders that worms fall asleep or wake up from the first, second slough, etc....

In the seventh day of the fifth age, the worm reaches its complete development, its weight is about 5 gr or 9.500 times bigger than the day of its birth, its length is 9 cm. It begins in decreasing the 9-th day.

The duration of every age or the complete breeding depends on the degree of heat and on the frequency of meals. The bombyx mori feeds exclusively on leaves of mulberry tree, which are spred on the racks formed with a wooden frame and on which the bottom, in trellis of reeds or iron wires, is covered with a sheet of strong paper.

 

Délitement

The meals of worms require an operation called " délitement", which goal is to change the litter of worms. This operation is made easily by means of a paper (papier à déliter: splitting paper) , borde with holes in which the size is depending on the age of worms, we place these paper sheets on the worms and we covers them with fresh leaves, worms do not delay rising by way of holes, this ascent takes place within one half an hour, then we removes the paper loaded of worms that we carries on a new rack.

We have to abandon some late worms stayed on the litter that we take car to carry right away outside the workshop.

The quantities of consummate leaves are for one ounce of 30 grams of seed, that means for 40 - 50.000 worms:

  • 1-st age, 5 in 6 kg
  • 2-nd age, 15 in 16 kg
  • 3-rd age, 51 in 52 kg
  • 4-th age, 156 kg
  • 5-th age, 900 kg

During the 1-st and the 2-nd age, we has to give finely cut leave at the same moment the distribution, the meals must be frequent and light; the leaves being soft, dries out quickly due to the high temperature of the workshop. It is necessary to renew meals every three hours.

From the 3-rd age, we can reduce the number of meals to 6 by 24 hours, except in the "frèzes" time, where we have to give intermediate meals. The name of "frèzes" is given, at certain periods of 3-rd , 4-th, and 5-th ages, during which worms eat with greediness.

The leaf must be cut less slim of age in age, till the end of the 4-th.

We must serve the complete leaf in the last age. The necessary space for worms is an object of appreciation, we have to care that they are not accumulated on the litter that is one of the causes of the fatal diseases which they contract. So, it is necessary to halve the racks according to the increase in weight of worms, every worm must always have a space three times bigger than the one it occupies motionless. The halving is made in the same way as the "délitement" with the "paper à deliter".

 

Afforestation

When the silkworm reached its complete development,( ie: towards the 8-th day of the 5-th age), we have to proceed to the afforestation or to the encabannage (in hutting) of the worms by forming around racks a sort of artificial hedge, with the dry heath, brooms or with the colza, warms climb in these twigs and choose a place in their suitability to spin their cocoon.

 

"Déramage"

The silkworm takes about 3 days to make its cocoon, but it is not allowed to déramer, that means to make the crop of cocoons before the 7-th day, so that work is complete for all the series. From this moment, it loses daily of its weight,so, there is interest, for the breeder, to sale as soon as possible. If the breeder wants to make his grainage (sedding) himself, it is at the time of the déramage that he has to choose the cocoons which he will let drill by the butterflies.

These cocoons must be chosen among those, which are better shaped the hardness at the pressure exercised between the thumb and the index, on two extremities; they must not be thrown far away in baskets to avoid damaging chrysalises in formation. It is about 3 days after the completion of the cocoon that the worm is completely metamorphosed into chrysalis.

Then about 15 days later, the butterfly is formed, and, if we had the care of killing the chrysalis before this last transformation, the butterfly would go out of its cocoon in piercing it; having as consequence to not be able to be spined.

 

Breathlessness of chrysalises

The purpose of this operation is not only to kill the chrysalis, but also its complete drying, so that it can not occur any more putrefaction, having as a result to stain the cocoons which would lose all their monetary value. Various systems are used, among which we shall describe the two following ones:

1- In the oven: The steam room, called vulgarly oven or "damper", is formed with a room in masonry, measuring approximately 2 m on all the faces; on two opposite lateral faces are arranged doors with two padded leaves to obtain a closing quite hermetic.
On the other hand we have a lorry with racks on which we arrange flat baskets filled with cocoons under a weak thickness, the lorry so loaded is pushed inside the oven, doors are closed, and a current of vapour is sprayed inside the steam room. After stay of about one half an hour chrysalises are killed. During this time it has been proceeded to the load of the opposite lorry in the aim to operate continuously, day and night , until exhaustion of provisions.
We understand that the breathlessness of chrysalises has to intervene quickly, because the papillonnage can begin 15 days after the forming of the cocoon. The cocoons chrysalises that were suffocated by this method go out of the oven completely wet as a result of the cooling of the vapour while opening the steam room. So, it is necessary to dry air them completely.
To do this operation, vast premises largely ventilated, called coconnières are arranged to receive racks on which are put cocoons in thin layers to allow a quickly evaporation and also to avoid the accident of the stained cocoons.

2- In box: This modern process has the big advantage on the precedent to cancel the coconnières, since the cocoons leave of the apparatus absolutely dry, the chrysalis, completely dried which allows to package right away the cocoons.
The apparatus consists mainly in 12 boxes with the bottom having put wire netting on; every box can contain 100 kg of cocoons, they are arranged on a single line over a ventilated warming room, temperature is maintained regularly in 83 ° during all the time of the operation.
We begins to fill the first box in which cocoons stay during an hour, at the end of this time we empty first box of cocoons in the second and we fill again the first. After the second hour we empty the second box of cocoons in the third and the cocoons of the first in the second, then we fill again the first box, so in succession until the twelfth.
From there they are directly put into bags and operation is ended. We can so by this process and with a single apparatus of 12 boxes, to suffocate the chrysalises of 2400 kg of cocoons in the 24 hours.

The butterfly

To go out of the cocoon in which it is prisoner, the butterfly unstuff some drops of an alkaline liquid which come unstuck the silk threads at one extremity of the cocoon, then with the paws it moves away the threads without breaking them and quite completly its jail. Most of the time, it is in the morning that the "butterflying" of cocoons occurs.

Immediately outside the male butterflies approach females and the coupling is realised. The duration of this coupling is variable and depends on the temperature, average is from 5 to 6 hours at a temperature of 20 °C.
The female separated from the male is put down on linen fragments measuring 15 cm length and 10 cm width and some moments after the laying begins, eggs stick on the cloth and it is in this state that we will have to preserve them , in a dry place and at a temperature of 12 ° about, till the next breeding.

 

"Seeding" or "Grainage"

It is of a huge importance to put in the incubation only healthy seeds and consequently exempt from any germ of diseases. For a long time we only sorted out carefully the cocoons which expected to be used for the seeding. In spite of this precaution it often appeared that the butterflies were bearing the germ of a hereditary disease, which was given to worms born from these contaminated seeds. Today, due to the researches of our illustrious M. Pasteur, the breeder can obtain himself or get himself seeds absolutely healthy.

 

The cocoon

The thread composing the cocoon is formed with 2 slimes secreted by the silkworm which are welded together by a gummy material called stoneware. The stoneware is the whole, gelatinous, waxy, coniferous and colouring materials which cover the fibroïne as a sheath. Slimes result from a liquid contained in the silky glands of the worm that solidify in the exit of the trunk. The silk thread consists so essentially of two different elements, the fibroïne or silk and the stoneware, which wraps and welds 2 slimes. Proportion between these two substances is on average 75 % of fibroïne and 25 % of stoneware, which is soluble in a boiling solution containing 25 % of soap of the silk weight.

The cocoon is egg-shaped, the average length thread is of 600 m. It is to be noted that the thread has a double thickness at the beginning of the cocoon with respect to its end. It needs 11 kg of fresh cocoons to obtain 1 kg of spun silk or 3 kg of dry cocoons.