Bombyx mori

Overview

Bombyx mori, commonly known as the domestic silk moth, is a special kind of moth that people have raised for thousands of years. These moths are important because their young, called silkworms, make silk. Silk is a soft and shiny material used to make 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 taken 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 hatch after about 14 days. The baby moths, called silkworms, eat white mulberry leaves and other mulberry plants. They grow and change five times before they become pupae.

The silkworms then make a cocoon from silk. Inside the cocoon, they change into pupae. The cocoon keeps them safe. When they are ready, they leave the cocoon and become adult moths. To get the silk without hurting the moths, people sometimes heat the cocoons to make the silk easier to use.

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

Research

Silkworms are small and easy to care for, so they help scientists learn about insects. Researchers have studied genes, smells insects use to find mates, hormones, brain structures, and how silkworms' bodies work.

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

Some scientists made a special silkworm that can produce a strong material like spider silk. Others made materials from silkworm silk that doctors can use in surgeries. Scientists are also using silkworms to find new medicines and learn more about harmful germs.

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 stay close to humans and be kept in crowded places. Unlike wild moths, domestic silk moths cannot fly, so humans help the males find mates. They also do not fear predators because they live only in captivity. These moths have lost their natural colors, making them pale, because they do not need to hide when people keep them safe. Because of these changes, domestic silk moths need 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. 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 very long and has many repeating parts. Some of its genes are special and help the moth make lots of silk and eat mulberry leaves.

In 2018 and 2022, more information about different silk moth strains was shared.

As food

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

• In Assam, India, they are boiled and eaten with salt or fried as a snack.
• In Korea, they are boiled and seasoned to make a snack called beondegi.
• In China, roasted silk moth pupae are sold by street vendors. The silkworm droppings are used in traditional Chinese medicine.
• In Japan, silkworms are served as tsukudani, boiled in a sweet-sour sauce with soy sauce and sugar.
• In Vietnam, they are boiled, seasoned, and stir-fried as a main dish.
• In Thailand, roasted silkworms are sold at markets and as packaged snacks.

In China, silkworms have been suggested for taikonauts as space food on long missions.

In culture

China

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

Vietnam

In Vietnam, there is a folk tale about silkworms. The story is about a kind housemaid who ran away from bad masters. She 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. After she passed away, she turned into silkworms to continue helping people.

Feeding

The domestic silk moth, Bombyx mori, only eats mulberry leaves from the Morus family. Scientists have studied what these moths need to grow by using special food made in labs.

There are five groups of important building blocks, called amino acids, that these moths need:

• If you take away some amino acids like lysine or leucine, the baby moths stop growing.
• Removing others like glutamate makes their growth slower later.
• Some amino acids, like proline, are not needed if you give the moths similar ones.
• The larvae can make some amino acids, like alanine, 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 silkworm and usually happens when silkworms are kept in cold, wet places. It does not spread to the eggs.

Another disease is called Grasserie, or nuclear polyhedrosis. It is caused by a virus and makes the silkworms look milky. 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 and look pale. This disease can be passed from mother moths to their eggs, so checking the moths carefully helps prevent it.

Flacherie makes silkworms look weak before they die. This sickness can be caused by viruses or bad food.

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