Bombyx mori

Bombyx mori, commonly known as the domestic silk moth, is a special kind of moth that people have taken care of for thousands of years. These moths are very important because their young, called silkworms, make silk, a soft and shiny material used to make beautiful clothes and other things. Silkworms love to eat leaves from a plant called white mulberry, and sometimes they eat leaves from other mulberry plants too.

Unlike wild moths, domestic silk moths need help from people to have babies. This is because people have been carefully choosing and taking care of these moths for so long that they can’t survive without us. Wild silk moths are different; they can live on their own, but they don’t make as much silk.

The practice of raising silkworms to get silk is called sericulture, and it has been done for at least 5,000 years, starting in China. From there, it spread to places like India, Korea, Japan, and later to other parts of the world. Domestic silk moths originally came from China, not from Japan or Korea. Over time, these moths changed—they lost their colors and their ability to fly, making them even more dependent on humans.

Types

Mulberry silk moths are grouped into three main types based on how often they have babies each year. Univoltine moths, found in Europe, only have one group of babies each season. Their eggs sleep through the winter and wake up in spring. Bivoltine moths live in East Asia and have two groups of babies each year because it’s warmer there. Polyvoltine moths are found in tropical areas and can have up to eight groups of babies in a single year because their eggs hatch quickly. These moths are very sensitive to changes in light, temperature, and humidity, which affect their growth.

Description and life cycle

Eggs of the domestic silk moth take about 14 days to hatch into larvae. These larvae, known as silkworms, love to eat white mulberry leaves and can also eat other types of mulberry plants. They go through five stages before they turn into pupae.

After several changes in their bodies, the silkworms make a cocoon from raw silk that they produce. Inside this cocoon, they change into pupae. The cocoon protects them during this time. When they are ready, they break out of the cocoon and become adult moths. To get the silk without harming the moths, people often boil the cocoons, which makes the silk easier to use.

Adult silk moths have a wingspan of about 3–5 cm and a white, hairy body. Females are larger than males. These moths do not eat and cannot fly far because their bodies are too heavy for their small wings.

Research

Because they are small and easy to care for, silkworms have been very helpful for scientists studying insects. Researchers have learned important things about genes, smells that insects use to find mates, hormones, brain structures, and how silkworms' bodies work.

Scientists have also studied the genes of silk moths to see if they can change them. They keep many different types of silkworms and have found over 400 special traits passed down through families. Some scientists have made silkworms that can eat food besides mulberry leaves, which are usually their favorite. Other researchers are trying to change silkworms so they can make useful medicines instead of silk.

One group of scientists made a special silkworm that can produce a strong material like spider silk. Others have made materials from silkworm silk that doctors can use in surgeries to help fix damaged parts of the body. Scientists are also using silkworms to find new medicines and to learn more about harmful germs that can make people sick.

Domestication

The domestic silk moth, B. mori, is different from wild silk moths. It has a bigger cocoon, larger body, grows faster, and digests food better. It can tolerate being around humans and being kept in crowded places. Unlike wild moths, domestic silk moths cannot fly, so humans help the males find mates. They also lack fear of predators because they live only in captivity. These moths have lost their natural colors, making them pale, because camouflage isn’t needed when they are kept safe by people. Because of these changes, domestic silk moths depend completely on humans to survive and cannot live in the wild. Their eggs are placed in special boxes called incubators to help them hatch.

The earliest proof that people began raising silk moths comes from ancient China more than 5,000 years ago. In those times, people also raised fish called common carp in ponds near their silk farms. The fish were fed with silk moth larvae and their waste, allowing people to raise both silk moths and fish at the same time.

Raising silk moths is done to improve the worms for business reasons. Goals include making more eggs, healthier larvae, more cocoons and silk, and better resistance to sickness. Healthy larvae lead to a good crop of cocoons. Health depends on things like a good rate of turning into pupae, fewer dead larvae, a shorter time as larvae, and bluish-colored larvae, which are healthier. The amount of cocoon and silk produced depends on how well the larvae turn into pupae and their weight. The quality of the cocoon and silk depends on many things, including the genes of the moths.

In the U.S., some teachers bring domestic silk moths into the classroom for science projects. Students can watch the whole life cycle from eggs to larvae to pupae to moths. This activity is also used in schools in China, South Africa, Zimbabwe, Iran, and Taiwan.

Genome

In 2008, scientists finished mapping the full set of instructions, or genome, of the domestic silk moth. This genome is about 432 million pieces long and has many repeating parts. Some of its genes are special and not found in other animals. These special genes help the moth make lots of silk and eat toxic mulberry leaves.

Later, in 2018 and 2022, more detailed pieces of information about different silk moth strains were shared.

As food

Silk moth pupae are edible insects and are eaten in some cultures:

• In Assam, India, they are boiled for extracting silk and the boiled pupae are eaten directly with salt or fried with chili pepper or herbs as a snack or dish. Live pupae may be eaten raw, boiled or fried.
• In Korea, they are boiled and seasoned to make a popular snack food known as beondegi (번데기).
• In China, street vendors sell roasted silk moth pupae. The silkworm droppings are secretions used in traditional Chinese medicine.
• In Japan, silkworms are usually served as a tsukudani (佃煮), i.e., boiled in a sweet-sour sauce made with soy sauce and sugar.
• In Vietnam, this is known as nhộng tằm, usually boiled, seasoned with fish sauce, then stir-fried and eaten as main dish with rice.
• In Thailand, roasted silkworm is often sold at open markets. They are also sold as packaged snacks.

In China, silkworms have also been proposed for cultivation by taikonauts as space food on long-term missions.

In culture

China

In China, there is a story about how people first found out about silk. An ancient empress named Leizu, the wife of the Yellow Emperor, was drinking tea under a tree when a silk cocoon fell into her tea. She noticed the silk and saw a small larva, which is the baby silkworm. She shared this discovery with others, and silk making became well-known.

Vietnam

In Vietnam, there is a folk tale about silkworms. The story tells of a kind housemaid who ran away from bad masters and lived in the mountains, where she was safe. A god from the heavens tried to harm her, but she was protected. She used a net to stay safe and later turned into silkworms after she passed away, so she could continue to help people.

Feeding

The domestic silk moth, Bombyx mori, only eats mulberry leaves from the Morus family. Scientists have learned which special building blocks, called amino acids, these moths need to grow by using special food made in labs.

There are five groups of these amino acids:

• If you take away certain ones like lysine or leucine, the baby moths stop growing completely.
• Removing others like glutamate slows down their growth later.
• Some amino acids, like proline, aren't absolutely necessary if you give the moths other similar ones.
• The larvae can make some amino acids, like alanine, all by themselves.
• And a few, like tyrosine, the larvae don’t need at all.

Diseases

Silkworms can get sick from different things. One sickness is caused by a fungus called Beauveria bassiana. This fungus can destroy the whole silkworm body and usually happens when silkworms are kept in cold, wet places. It does not spread to the eggs because infected silkworms cannot become moths.

Another disease is called Grasserie, or nuclear polyhedrosis. It is caused by a virus and makes the silkworms look milky or hang up when they are growing. If eggs are infected, cleaning them before they hatch can help stop the disease. This sickness can happen if the place where silkworms are kept is not clean.

Pébrine is a disease caused by tiny parasites. Sick silkworms grow slowly, look pale, and have tiny black spots. This disease can be passed from mother moths to their eggs, so checking the moths carefully helps prevent it.

Flacherie makes silkworms look weak and dark brown before they die. This sickness hurts the silkworm's gut and can be caused by viruses or bad food.

There are also several fungal diseases called Muscardine that can affect silkworms.