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Caterpillar Secrets

by Sue Smith Heavenrich

Fall is a great time to study caterpillars. This author offers a wonderful account of living nature study in her family.

"Do you study biology?" one of the high school students asked my children. She was curious about what homeschooled children studied.

"No!" stated my oldest, with all the authority he could muster. "We study caterpillars." On the drive home he asked, "What is biology anyway?"

"Life. The Universe. And everything," I responded. "Definitely caterpillars."

Like most scientific investigations, our studies of caterpillar behavior began with a simple question: How much can a single caterpillar eat? We were standing behind the house assessing gypsy moth damage to our trees. It was a bad year, and the infestation was so high you could hear frass dropping on leaves like rain. ("Frass is caterpillar poop," I explained.) Bits of pale green leaves littered the ground, crumbs dropped from the herbivorous gluttons devouring the forest canopy.

"Good question," I replied. "How can we find out?" A quick search of our reference books indicated that yes, gypsy moths could in fact defoliate entire forests. But not one word on how much a single hungry larva could eat in a day. Soon my curious naturalists were collecting the dark, hairy gypsy moth caterpillars for their research.

"We'll put them in a jar with leaves and see how much they eat," explained Toby and he began picking as many un-munched leaves as he could find. As they began to put caterpillars and leaves into jars, they realized that this would not really answer their question.

"Each caterpillar needs its own jar."

"How can we measure how much of the leaf gets eaten?"

"We could weigh it today, then weigh what's left tomorrow."

I pointed out that the leaves would lose moisture overnight, and that might change their weight as well. Eventually they hit upon the idea of tracing the leaves onto paper, then comparing how much was left over with the original tracing. To make it "more scientific," we used metric graph paper with centimeter squares. Now we could approximate leaf area by counting square centimeters.

If we want our children to learn about science, we must encourage them to investigate their world. This is, after all, what scientists do. Science is a process of inquiry, not a body of facts to be learned from books. It's about asking questions, designing ways to learn the answers, and when those tests fail, re-designing new experiments. It's about "messing around". There is no way you can do science without getting your hands on it.

Our science studies are a natural outgrowth of our interests and involve us in the real world. This is the greatest advantage to homeschooling. We are not experts, so we have to accept the risk of failure as an essential ingredient in our experiments. Mistakes are great, I tell the kids. That's how we discover new things. It's OK, in our science lab, to say, "Oops... guess that doesn't work."

But, back to caterpillars. In late summer the monarch butterflies have finally found our hayfield, and we find hundreds of the white, yellow and black-striped larvae busy munching milkweed leaves. But we never see a chrysalis in the field.

"Maybe they go to a protected area," suggests one of the kids. We look around. We could put a soccer field between the milkweed patch and the nearest hedgerow.

"Can they really walk that far?" we wonder. Next thing I know, the kids have collected half a dozen caterpillars and are designing a monarch speedway on the kitchen floor.

"We're going to let them go, and time them for a minute. Then we'll measure how far they've gone." My kids look quite official with a stopwatch and notepad. The problem with caterpillars, they soon discover, is that they don't walk in a straight line. Eventually my kids hit upon the idea of laying out a huge sheet of paper and tracing the caterpillar paths. They test each caterpillar twice, then I show them how we can do an average.

Eighteen. That is the number of inches the average monarch caterpillar crawls in a minute. Almost the length of a four year old's stride. We play around with the calculator and discover that at this rate it will take two and a half days to walk a mile.

A couple years later we're watching woolly bears cross the road. Woolly bears are cute, fuzzy brown caterpillars with broad black bands. They're active in the fall, and ubiquitous, I tell them. Does that mean they forecast the weather? Toby asks. ("Ubiquitous" is a wonderful word for an eight-year-old to learn.)

"Do you suppose they're faster than monarchs?" the other asks, and we're off to the caterpillar races again. This time we try a new idea - a circular racing arena drawn on a large piece of butcher paper. It looks like a huge archery target, each circle's radius one foot longer than the one inside it. The children release the caterpillars in the center of the arena, then time them for one minute. Woolly bears crawl at a speedy 44 inches per minute. In a mile race, they'd beat the monarchs by nearly a day and a half.

The children noticed that the woolly bears seemed to travel in one particular direction. "Maybe they have something in their brain that senses the earth's magnetic field," one suggested. Using a compass, they labelled the arena N, E, S, W. "South. They're definitely walking south."

The next morning we noticed woolly bears on the road heading in the opposite direction. "Do you suppose it could be the light that they're going to?" I asked. Time to try a new idea.

I brought the question to a couple of classrooms in the school where I volunteer. Perhaps more people working with more caterpillars would give us more information. First we tried darkening a room to see how the woolly bears traveled in darkness. We covered flashlights with red cellophane so we could see the caterpillars. The woolly bears seemed to go in all directions. Then someone accidentally knocked open the curtain. In that momentary flash of light, the caterpillars turned towards the windows!

"Can we design a test that will help us determine that it is the light they are moving to?" I asked. Someone came up with the idea of a "choice tube". Take two paper towel tubes and push them together. Cover one end with dark paper and leave the other end open. Now open the tube, plop a woolly bear in the middle, then close it up. After a few minutes look inside to see where the woolly bear went. A couple days of testing convinced us that the caterpillars move towards light.

The thing about caterpillars is that they eventually turn into butterflies. The thing about exploring science with my children is that our projects undergo metamorphosis too, evolving into new ideas. Now we want to know whether butterflies prefer certain colors of flowers. This summer you'll find us putting out clear yogurt lids of sugar water on a table covered with squares of brightly colored paper.


  • The Insect Book, A Basic Guide to the Collection and Care of Common Insects For Young Children, by Connie Zakowski. Rainbow Books, 1997.
    Includes information on how to capture insects and gather their food. Also has a guide to caterpillars and what butterflies they will become.

  • The Butterfly Book: A Kid's Guide to Attracting, Raising, and Keeping Butterflies, by Kersten Hamilton. John Muir Publications, 1997.
    Photos of butterflies and their larvae, along with range maps. How to feed butterflies, how to fix broken wings, and lots of other useful and fun information.

  • Caterpillarology, by Michael Elsohn Ross. CarolRhoda, 1997.
    A "must read" for the seriously interested. Facts, natural history, and ideas for research. Too bad it wasn't around when we were doing our studies!

1999, Sue Smith Heavenrich

This article first appeared in Home Education Magazine (July-August 1999) and is reprinted here with permission of the author.

Growing Together Family Learning Newsletter, Vol. 1, No. 2, page 5

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