Silkworms are the easiest eggs I have ever hatched with students in my classroom. You’ll be able to observe the entire life-cycle from egg hatch to egg laying, and since the moths don’t fly, and the larvae stay on the leaves, you don’t need any special equipment or home to keep them in. All you will need is a plastic or Styrofoam tray, some paper towels, and access to mulberry leaves. (Silkworms are caterpillars, not worms, by the way.)
Finding mulberry leaves may be the only difficult part of the task. Early in my career I had to go to a local park to collect leaves, but in the last decade or so almost every school I worked at had a mulberry tree on the site. (I planted a mulberry tree at a couple of the schools where I worked, with permission of course, to make life easier in the future. I have one in my yard now. Get a fruitless white mulberry if you choose to do this.) You can also buy silkworm food, which you may have to do anyway to start early enough, but it’s not nearly as natural as using mulberry leaves.
The first time you hatch these eggs, you’ll have to buy them, unless you have a friend who has some and will give them to you. But from then on you can collect the eggs that are laid, keep them in your refrigerator, and take them out the next spring whenever you’re ready to start again. You can get them from Carolina Biological Supply, and other science supply stores.
It takes 3 to 4 months for the cycle to complete. In nature, silkworm eggs hatch when mulberry trees begin to bud. In much of the country that doesn’t give enough time to complete the cycle by the end of the school year. You’ll need to start the process in mid February or early March to complete the cycle by early June. (You can speed up the process by keeping your classroom warm all the time.) However, even if your students are unable to see the complete cycle, it’s still a worthwhile activity as they watch the eggs hatch and the larvae grow. And at the end you’ll have the eggs you need for next year, and can start the process any time, as long as you have food available (mulberry trees don’t begin to leaf out until mid March, or later, depending on where you live).
Here’s what to do:
- Set up an observation area in your classroom. Put books and pictures in the center.
- Line a plastic tray with paper towels, and set the eggs on the towels. Put a fresh mulberry leaf on the tray near the eggs, which will start to hatch in a week or two.
- Each day have a couple of students clean the tray and feed the larvae. Move the leaves onto the table, and replace the paper towel. Fold the corners of the paper towel in toward the middle to collect all the dung, fold it all up, and put the paper towel a trashcan. It is not very messy. Then put the old leaves, with the larvae on them, back onto the fresh towel. Put the fresh leaves on top of the dry leaves, and the larvae will climb onto the new leaves. Leave the old leaves in the tray until you are SURE there are no caterpillars on them. If you have to remove tiny hatchlings from the old dead leaves, use a watercolor paintbrush. Gently pick them up with the tip of the paintbrush and put them on a fresh leaf. Once the silkworms are about an inch long, the children can gently peel them off the old leaves, and place them on the new leaves. The caterpillars will molt 4 times during the process.
- When the caterpillars are 3 to 4 inches long (about the size of your ring finger), they will begin to spin their cocoons. I like to provide an egg carton for this process. It gives them plenty of attachment points, and separate spaces. Just open the carton and place it on the tray, along with a few leaves in the top. They’ll climb into it. You’ll be able to see the worms inside their cocoons at the beginning of this process. It’s very interesting.
After 2-3 weeks the moths emerge from their cocoons. They will mate as soon as a mate is available. The eggs will show up within a day or two. At first they will be lightly yellow, but as the larvae began to grow they will turn black. This usually takes a few days. If you don’t put the eggs into the refrigerator, they will begin to hatch within a couple of weeks. Placing them in the refrigerator simulates winter in their native environment (China and Japan). The moths don’t eat or drink, and they die after laying the eggs. You can keep the cocoons to display next year, and for your students to “dissect.” If you boil them in water, the silk will unwind, however it won’t be in one long piece because of the hole in the cocoon.
There are lots of things to do while the eggs are hatching and the larvae are growing:
- Record observations in an observation notebook.
- Take photographs each day and add to the observation notebook.
- Use the photographs for sequencing activities.
- Make a poster of the life cycle of the silkworm.
- Measure the larvae each day and record on a graph.
- Cut the images from the photographs to make magnetic board or flannel board story characters.
- Write a process piece about the development of silkworms.
- Compare the size of the mulberry leaves with the growth of the silkworms.
- Compare the life-cycle of the silkworm with that of other insects and animals.
- Write fiction and nonfiction pieces with a silkworm focus or characters.
- Make finger puppets for each step of the life-cycle process.
- Create a silkworm life cycle finger play with your students.
- Paint images of the mulberry tree at different seasons.
- Observe and draw pictures of each process stage.
- Make leaf prints using mulberry leaves.
- Make crayon rubbings of mulberry bark.
Hatching silkworms is a very up-close and personal activity for students, and is just as appropriate for 3 year olds as for 6th graders!
What are your favorite activities to correlate with life-cycle studies?