Silkworms and Their Life Cycle: The Foundation of Sericulture

Silk is often called the “queen of textiles,” and for good reason. Behind every shimmering saree, every fine silk tie, lies the extraordinary journey of a tiny insect – Bombyx mori, the mulberry silkworm. Understanding how this insect lives, grows, and spins its cocoon is not just a matter of biology. It is the very foundation of sericulture, the age-old practice of silk farming that continues to sustain millions of rural families across Asia today.

What is Bombyx mori and why does it matter?
The four stages of the silkworm life cycle
Stage 1: The egg
Stage 2: The larva
Stage 3: The pupa (cocoon stage)
Stage 4: The adult moth
From cocoon to cloth: the silk harvesting process
Stifling
Sorting and cooking
Reeling and throwing
The mulberry connection: why diet determines silk quality
Women and sericulture: the backbone of a rural industry
A note on ethics: the debate around conventional sericulture
Why understanding the life cycle matters

What is Bombyx mori and why does it matter?

Bombyx mori, commonly known as the mulberry silkworm, is the most commercially important silk-producing insect in the world. Sericulture – the cultivation of silkworms for silk production – is believed to have originated in ancient China, with records of silk use dating back to around 2700 BCE. Over thousands of years of selective breeding, B. mori has become entirely dependent on humans for survival. It no longer exists in the wild, cannot fly, and has even lost its natural coloration – all traits traded away in exchange for an extraordinary ability to spin high-quality silk.

The silk it produces is a proteinaceous fibre secreted during the larval stage and is regarded, across cultures, as one of the most luxurious natural materials. The rearing of silk moths and the production of raw silk is collectively known as sericulture. At the heart of this industry is a precise, four-stage life cycle – egg, larva, pupa, and adult – each stage playing a distinct and critical role.

The four stages of the silkworm life cycle

Stage 1: The egg

Everything begins with the egg. After fertilisation, each female moth lays approximately 300 to 400 eggs, placed in clusters and fixed to surfaces by a gelatinous secretion. In commercial sericulture, these eggs are laid on waxed paper, collected, and treated with a 2% formaldehyde solution to prevent disease. They are then incubated under carefully controlled conditions of temperature and humidity. In multivoltine races found in tropical areas like India, the egg stage lasts around 9 to 12 days, while in uni- and bivoltine races common in temperate zones, it may extend to 11-14 days.

Stage 2: The larva

The larval stage is where the real action happens – and where the rearer’s work is most demanding. Once hatched, the tiny caterpillar is only about 3 mm long and is popularly called the first instar. The larva is a voracious eater; in the early stages it is fed chopped young mulberry leaves, but as it matures, whole and fully developed leaves are provided. This exclusive diet on mulberry leaves directly influences the quality of the silk the worm will eventually spin.

During the larval period, the worm moults – sheds its skin – four times, dividing the larval life into five distinct stages called instars. Each moult allows the larva to grow rapidly. By the time it reaches its fifth and final instar, it has grown to nearly 10,000 times its hatching weight – all within a span of about 20 to 28 days. This phenomenal growth rate makes careful rearing and hygiene absolutely essential during this stage.

When the larva is fully mature, it stops feeding, excretes watery faeces, and begins to wander – a clear signal that it is ready to spin its cocoon.

Stage 3: The pupa (cocoon stage)

The cocoon stage is where silk is actually produced. The fully grown larva begins to secrete a clear, sticky fluid from its salivary glands through a narrow pore called the spinneret, which hardens into a fine, continuous silk filament on contact with air. The worm moves its head from side to side in a rhythmic figure-eight motion, wrapping itself in layer after layer of silk. The resulting cocoon is formed from a single continuous filament, from which over 900 metres of usable silk thread can be obtained.

Inside the sealed cocoon, the larva undergoes complete metamorphosis – transforming its body into a pupa, breaking down old organs and developing the wings, antennae, and reproductive structures of the adult moth. The pupal stage lasts approximately 10 to 15 days. In commercial sericulture, however, the pupae are killed before the moth can emerge, because an emerging moth secretes a proteolytic enzyme that breaks the silk filament, making continuous reeling impossible.

Stage 4: The adult moth

If allowed to complete its cycle naturally, the adult moth breaks through the cocoon and emerges ready to mate. Adult moths have lost their ability to fly and do not feed, devoting their short lives entirely to reproduction – typically living only 3 to 5 days. In sericulture, a small number of moths are always allowed to complete this stage so they can lay the next batch of eggs, continuing the production cycle. The rest of the cocoons are harvested before emergence to preserve the silk.

From cocoon to cloth: the silk harvesting process

Once cocoons are ready for harvest, they go through a series of careful processing steps before becoming the silk fabric we recognise.

Stifling

The first step after harvest is stifling – killing the pupa inside the cocoon to prevent moth emergence. This is done by exposing cocoons to steam, dry heat, or boiling water, a process known as stifling. Hot air treatment at around 60-70°C for several hours is the most common method in modern facilities. Proper timing is critical: cocoons must be stifled within 2 to 3 days of spinning, before the pupa develops further.

Sorting and cooking

After stifling, cocoons are sorted by quality – selecting for compact shape, uniform colour, and proper shell weight. Defective or damaged cocoons are separated out as they cannot yield a continuous filament. The sorted cocoons are then placed in hot water – a process called degumming – which softens and dissolves the sericin (the natural gum holding the silk fibre together), freeing the filaments for reeling.

Reeling and throwing

Reeling is the process of unwinding the silk filament from the softened cocoon onto a reel. Because a single filament is too fine for practical use, several single filaments are combined and twisted together into a thread in a process called “throwing,” which produces yarn of different strengths depending on the amount and direction of twist applied. This raw silk yarn is then washed, degummed, dyed, and woven into the final fabric. It takes approximately 100 metres of silk filament to produce a single strand, with multiple strands combined to build a usable thread.

The mulberry connection: why diet determines silk quality

Bombyx mori is what biologists call a monophagous species – it feeds exclusively on mulberry leaves. The nutritional composition of mulberry leaves directly affects the texture and strength of the silk fibres the worm produces, making leaf quality a science in itself. This is why sericulture is inseparable from moriculture – the cultivation of mulberry plants. Farmers must maintain healthy mulberry plantations alongside their silkworm rearing operations to ensure a consistent supply of fresh leaves throughout the larval stage.

Because the silkworm’s body has been so thoroughly adapted to captivity through centuries of selective breeding, the larvae can no longer cling to plants at gravity-defying angles and must be fed by hand – making human involvement in every stage of rearing non-negotiable.

Women and sericulture: the backbone of a rural industry

Sericulture is not just a biological process – it is a social and economic one. In India and across South and Southeast Asia, women are the primary workforce behind silk production at the farm level. The nature of the work – rearing silkworms at home, monitoring feeding schedules, and handling delicate cocoons – fits naturally within the rhythms of rural household life, giving women a pathway to income without requiring them to leave their homes.

In India, it is estimated that sixteen people gain employment from every hectare of a mulberry farm, providing income to family members regardless of their skill level. Sericulture is practiced in over 52,000 villages across India, generating livelihoods for nearly 9.48 lakh families. Women make up a substantial share of this workforce – in many districts, nearly 60% of the sericulture labour force consists of women, either as family members or hired workers.

Sericulture is intensively practiced in states such as Jammu and Kashmir, Himachal Pradesh, Assam, West Bengal, Karnataka, and Tamil Nadu, where it creates employment and improves the economic conditions of small and marginal farmers. For women in these regions, participation in sericulture goes beyond income – it is linked to greater decision-making power within the household, access to skills training, and connections to cooperative networks and government support programs.

Research from southern India shows that sericulture has allowed women to gain economic independence and contribute to household income, improving their status both within the family and in the broader community. Skills in silkworm rearing, silk reeling, and weaving are often passed down through generations, with mothers training daughters in practices that have sustained communities for centuries. Women’s precision and patience make them particularly effective at silkworm handling – a task that demands consistent attention and care throughout the 20-plus days of the larval stage.

A note on ethics: the debate around conventional sericulture

The killing of pupae to harvest silk has not gone without scrutiny. Animal welfare advocates have long criticised the practice of boiling cocoons with living pupae inside, and Mahatma Gandhi opposed it on the basis of the ahimsa principle of non-violence, which led him to promote cotton and Ahimsa silk – silk made from cocoons of wild silkworms allowed to complete their life cycle before harvesting. Today, there are growing efforts around organic sericulture, Ahimsa silk production, and even lab-grown silk as alternatives. These are still niche, but they signal a broader conversation the industry is beginning to take seriously.

Why understanding the life cycle matters

For anyone entering the field of sericulture – whether as a farmer, researcher, or policy professional – a thorough understanding of Bombyx mori‘s life cycle is not optional. Every management decision, from the timing of egg incubation to the temperature of stifling chambers, flows directly from the biology of this insect. The larval stage determines silk quality; the pupal stage determines harvest timing; the adult stage closes the reproductive loop. Miss a step, and the entire crop can fail.

At the same time, sericulture is far more than a technical enterprise. It is a living tradition, shaped over millennia by communities – especially women – who have built detailed, practical knowledge of the silkworm’s needs through hands-on experience. That combination of biological precision and human skill is what makes silk genuinely remarkable, and what makes sericulture worth understanding deeply.

What do you think? Given how central women are to sericulture at the farm level, how should training and technology programs be designed to specifically address their needs and constraints? And as ethical concerns around conventional silk production grow, do you think Ahimsa silk or lab-grown alternatives can realistically scale to meet global demand?

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References

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Table of Contents

What is Bombyx mori and why does it matter? 🔗

The four stages of the silkworm life cycle 🔗

Stage 1: The egg 🔗

Stage 2: The larva 🔗

Stage 3: The pupa (cocoon stage) 🔗

Stage 4: The adult moth 🔗

From cocoon to cloth: the silk harvesting process 🔗

Stifling 🔗

Sorting and cooking 🔗

Reeling and throwing 🔗

The mulberry connection: why diet determines silk quality 🔗

Women and sericulture: the backbone of a rural industry 🔗

A note on ethics: the debate around conventional sericulture 🔗

Why understanding the life cycle matters 🔗