Life History of Silk Moth: Introduction, Various stages, Processing of Silk

When a female silk moth lays eggs, the life cycle of the silk moth begins. The caterpillars or larvae of the silk moth are hatched from the silk moth’s eggs. Silkworms produce pupa by feeding on mulberry leaves. To keep itself alive during the pupa stage, the silkworm weaves a net around itself. Let’s learn everything about the Life History of Silk Moth in detail.

Fibres are an extremely thin thread of natural or artificial substances used to make fabrics by turning them into yarns. Based on the origin, fibres are classified into two types: natural and synthetic. Fibres such as cotton, wool, and silk are extracted from plants and animals. Hence they are natural fibres. Whereas nylon, rayon, etc., synthetic fibres are manufactured in laboratories by various chemical processes. Among all-natural fibres, silk has a fascinating history and origin. Continue reading to know more.

Silk

On important occasions, we all notice our mother wearing a lovely silk saree. Among all the materials used in the textile business, silk is one of the most popular and expensive. However, we should study where these lovely fabrics come from! Silk is a type of animal fibre obtained by the silkworm, a type of insect. Bombyx mori is the scientific name for the silkworm. It’s amazing to think that such a small creature can produce such long threads!

Silk History

Silk has an ancient history that started in around \(2640\) BC from China. A legendary Empress of China named Si-Ling-Chi discovered silk as a fibre woven into royal fabrics. Soon this beautiful fibre got popularised and was commercialised to various parts of the world.

A famous route named ‘silk route’ stretched from Asia to the Mediterranean that passed over China, India, Persia, Arabia, Greece, and Italy emerged because of the substantial silk trading that took place. Soon other countries, including India, also started manufacturing their silk.

Based on its lustre and texture, silk is classified into various types such as Mulberry silk, Eri silk, Tussar silk, and Muga silk. Among all, Mulberry silk is the most famous one. Silkworms lay eggs on mulberry leaves, and their life cycle starts from this stage. The process of rearing silkworms for the production of silk is known as ‘sericulture’.

Life History of Silk Moth

The life history of Silk Moth diagram is given below:

Timespan of the life cycle of silkworms ranges from \(6\) to \(8\) weeks. At a time, the female silk moth lays about \(300\) to \(400\) eggs. The caterpillars or silkworms come out as the eggs hatch. This stage is known as the larval stage. The silkworm feeds on mulberry leaves, gets nutrients from them that flow into their bloodstream, and grows as a pupa.

In this stage, the silkworm secretes fine filaments from two silk glands located on its head. These thin filaments are made of a protein that hardens to form silk fibres when exposed to air. The silkworm deposits filaments in concentric layers around its body by spinning its head in the pattern of eight, forming a structure called the cocoon. The silkworm takes around three to seven days to prepare the cocoon, formed by about \(20-40\) concentric layers of a single thin thread. Inside the cocoon, the silkworm develops and enters the second stage of its life, i.e., ‘the pupa stage’, and then in the final stage, it becomes an adult moth. Silk threads are acquired from the cocoon of the silkworm.

Stages of Life History of Silk Moth

The life cycle of a silkworm follows the order: Egg\(\to\) Silkworm\(\to\) Pupa\(\to\) Adult Moth. Let’s have a detailed discussion on each and every stage of the life cycle of the silkworm as students will be asked to explain the life history of silk moths.

1. Egg

After mating, the female silk moth lays around \(300\) to \(350\) eggs at a time that appear as tiny dots on Mulberry leaves. Silkworm moths mostly reproduce only once each year, but a warm and moist climate may increase its rate to some extent. The eggs hatch in suitable conditions after ten days when the adult moth has laid them. From the eggs, tiny silkworms emerge.

2. Larva Stage

The silkworm or caterpillar that comes out of the hatched egg is covered in black hair and feeds on the mulberry leaves from where they get nutrition for growth. In the larva stage, or caterpillar stage, the silkworm exfoliates four times before going into the pupa. Firstly, the head of the silkworm turns a bit darker than the rest of its body. Each time it exfoliates, it sheds the old skin and grows a larger one. After the first exfoliation, the young silkworm sheds its hair and appears as a white, smooth and soft caterpillar. The larva stage lasts between \(24\) and \(30\) days.

3. Cocoon

Cocoon is the best commercial source of silk fibres. Silk fibres that are spun into cocoons are made up of fibroin proteins, forming a sericin covering. This wet or moist covering binds the fibres together and behaves as the non-woven composite matrix phase for the cocoon.

The silkworms secrete a very fine filament made of fibroin protein from two glands on its head which, on exposure to air, gets solidified and becomes silk fibres that are almost \(1\) kilometre long! The silkworm deposits filaments in concentric layers around its body; by spinning its head in the pattern of eight for around \(48\) hours, the silkworm completely covers itself, forming the cocoon.

4. Pupa Stage

Inside the cocoon, the silkworm develops into a pupa. This is the stage between larvae and adult moths. After \(14-15\) days, the pupa emerges from the cocoon as an adult moth. But for obtaining silk, this stage has no importance because cocoons are dived into boiling water, and silk threads are unwounded from cocoons.

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5. Adult Moth

After \(10-14\) days of developing into a moth in its cocoon, the Silk-Moth comes out of the cocoon and will excrete a brownish fluid while emerging. Silk-Moths cannot fly. Male and female silk moths can be easily separated as female silk moths have larger abdomens and males have smaller abdomens. After mating with the male moth, the female moth will lay eggs and die. In this manner the life cycle of silkworms continues.

Silk: Fibre to Fabric

Though silk dates back thousands of years ago, it is still one of the most beautiful, lustrous, delicate, and expensive fabrics. Here is the step-by-step method of silk processing.

1. Sericulture – The process of rearing silkworms for extracting silk fibres from the harvested cocoons is known as sericulture.
2. Thread Extraction – Once silkworms form cocoons on which silk fibres are spun, they are put in hot boiling water to soften and dissolve the gum that is holding them. This is a significant step in the silk production process as it ensures the continuity of each thread without any breakage. Each thread is then reeled from the cocoon in individual long threads very delicately. The leftover sericin on the threads to protect the fibres during processing is later washed out with soap and boiling water.

3. Dyeing – To give beautiful colours to the fibres, they are dyed using various techniques with different desired colours. Silk fibres are mostly dipped in a dye bath during this process to soak up the colours.

4. Spinning – The spinning process essentially unwinds the dyed fibres onto a bobbin to make silk yarns so that they are ready for weaving. This can be done in many traditional ways, like hand-spinning to ring-spinning or by spinners.

5. Weaving – Weaving is the process in which two sets of fibres are interlaced to form a strong and uniform piece of cloth. The silk fibres come together to form silk fabrics. Fibres are woven using weaving machines; after this step, fabrics are all ready for making dresses from them.

6. Finishing – After weaving, digital printing and finishing are done on fabrics and ready for use. Finishing a piece of silk gives it that highly lustrous appearance for which it is so commonly known.

Summary

In brief, the importance of silkworms to make silk fibres can be well understood by learning the entire procedure of silk extraction. Sericulture is an ancient science, and the modern age has not brought many changes to silk manufacture.

However, various man-made fibres such as polyester, nylon, and rayon have replaced silk in many criteria. But many of the unique qualities of silk cannot be replaced. As the female silkworm lays eggs on mulberry leaves, the development of this tiny creature starts. They enter into the larva stage. In this stage, these creatures are well known as silkworms or caterpillars. They develop a protective covering known as a cocoon to develop into a pupa.

During this process, silk spun by the silkworm starts as a liquid secretion. This liquid solidifies into a fibre on exposure to air. This stage is very critical as the pupa grows; they will break the cocoon to come out. So, to extract long, continuous threads, cocoons are emerged in boiling water to extract silk threads from them. The whole life cycle ranges from \(6\) to \(8\) weeks that includes four main stages: Egg \(\to\) Larva / Silkworm \(\to\) Pupa \(\to\) Adult.

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FAQs on Life History of Silk Moth

Q.1: What is the life span of a silk moth?
Ans: The life span of a silk moth ranges from \(6\) to \(8\) weeks. The entire life cycle starts from eggs and ends till adult moths are grown to reproduce again.

Q.2: What are the main stages in the life history of silk moths?
Ans: The life cycle of a silkworm consists of the following stages: Egg\(\to\) Silkworm\(\to\) Pupa\(\to\) Adult Moth. The period of the life cycle of silkworm ranges from \(6\) to \(8\) weeks. The female silk moth lays about \(300\) to \(400\) eggs at once. The caterpillars or silkworms come out as the eggs hatch. This stage is known as the larval stage. In this stage, the silkworm enters the pupa stage. It secretes fine filaments from two silk glands located on its head—the silkworm deposits filaments in concentric layers around its body by spinning and forming a cocoon structure. Inside the cocoon, the silkworm develops into a pupa, and then in the final stage, it becomes an adult moth.

Q.3: Where do silk moths lay eggs?
Ans: The female silk moth lays eggs on the mulberry leaves. The eggs are covered with a gelatinous secretion that helps them to stick to the leaves. Once silkworms emerge out of the hatched eggs, they feed on mulberry leaves and gain nutrition for their growth. Silkworm moths mainly reproduce only once each year, but a warm and moist climate may increase its rate to some extent. The eggs hatch in suitable conditions after ten days when the adult moth has laid them. From the eggs, tiny silkworms emerge.

Q.4: How many eggs can a female silk moth lay?
Ans: The female silk moth lays about \(300\) to \(400\) eggs that hatch in around \(1\) to \(2\) weeks under a warm and moist climate.

Q.5: Which country is the birthplace of silk?
Ans: The birthplace or origin of silk is China. Silk has an ancient history that started in around \(2640\) BC from China. A legendary Empress of China named Si-Ling-Chi discovered silk as a fibre woven into royal fabrics. Soon this beautiful fibre got popularised and was commercialised to various parts of the world.