Silkworms

Reprinted from The Wild Times Teacher Connection v2n3, Spring 1997.

The cultivation of silkworms by humans has been going on for more than 4000 years. The making of silk fabric from the thread produced by these larvae of the silk moth was perfected in Asia. Domestication of this insect followed. The highly valued cloth became an important international trade item opening up routes of commerce through Asia to Europe. Today, silk is used in a wide variety of applications from medicine to space technology. The cultivation of silkworms is possible anywhere there are mulberry trees.

Raising silkworms in the classroom can be an interesting project that easily cuts across traditional curriculum lines. Investigating the role of silk in history and its importance in countries where it has been traditionally manufactured falls easily into the realm of social studies. Studying the life cycle of the insect is science. Measuring the growth of the larvae fits into math. Moreover, watching the behavior and the growth and development of these animals is fascinating for everyone, adults and children alike. It is a wonderful catalyst for learning.

Culture:

Growing silkworms in the classroom is easy to do as long as there is a supply of mulberry leaves. The common silkworm, Bombyx mori, which is readily available through science education supply houses, eats nothing but mulberry leaves. Fresh ones need to be available frequently, preferably every day. It is possible to purchase eggs or larvae. Eggs may be kept refrigerated to delay hatching. If this project is done in the spring, it is important to keep the eggs refrigerated until there are well-developed buds on the mulberry trees. It will take a week or more for them to hatch once they are removed from the refrigerator. This is enough time for the mulberry buds to become small leaves. Once the larvae hatch, may be kept in an open container such as a box or tray. They will not crawl away. Simply place leaves in the container and place the larvae on the leaves. Keep them at room temperature, but not in direct sunlight.

In about 40 days they will grow from tiny threadlike creatures to large fat caterpillars. They will increase in size about 10,000 times. When they are ready to pupate, they will stop eating and begin to look for suitable places to spin their cocoons. Placing egg cartons around the edges of their container provides this. The cups in the egg cartons are about the right size, and the larvae seem to find them satisfactory. About three weeks later, silk moths will emerge from the cocoons. They do not fly or eat. They look for mates, lay eggs, and die in just a couple of days. The eggs may be collected, and refrigerated until the following spring when the project can be repeated.

Some teachers like to harvest the silk. In this case, the cocoons are cooked to kill the pupae. Then, they are unraveled by placing them in warm water to dissolve the natural adhesive that is present.

Suggested Science Lessons:

With young children, simply observing and recording growth and development may be enough. Observing generates many questions, such as: Why don't they climb out of the box? Why do they shed their skins? Do they eat all the time? Do they ever rest? Would they eat anything besides mulberry? Experiment and find out.

Drawing and writing about what they observe are always good ways for students to record their observations. In addition, making a graph that documents growth might be appropriate. Measuring length is easy to do. Measuring weight, though, requires sensitive equipment. Older children might take the weight study to another level, and keep track of the weight of what the larvae eat as well. Then, they can compare that with actual body weight that is gained. The moths can be weighed again after they hatch.

Report on Your Work to TWO:

Send your write ups, drawings and photographs to The Wild Ones. If you have other suggestions for activities involving silkworms, send them to the Teacher Connection.

Lucy is a member of The Wild Ones Advisory Council, and teaches science at the Chestnut Hill Academy in Philadelphia, PA USA.

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