For the past few weeks, my daughter and I have been immersed in a common childhood ritual: observing the lifecycle of a caterpillar. Unlike many families, though, we didn’t get the caterpillar from a mail-order kit. Rather, it arrived in our apartment aboard a pink begonia plant that we’d bought at the local farmer’s market. When my daughter discovered the insect clinging to the underside of a leaf, it was love at first sight, and I didn’t have the heart to put it outside.

Eliza with the caterpillar (look closely at her hand) before it doubled in size

And so began a brief adventure in entomology that’s still going. What started as a skinny, inch-long creature quickly grew into a fuzzy brown and black smudge that looked to be about twice its original length and three times its original girth. All the while, our guest was eating through the begonia leaves at an astounding pace – and leaving an equally astounding amount of waste, in the form of little black pellet balls, all over my windowsill. My daughter, Eliza, however, was smitten. Every morning and every night, Eliza, who is 5, would pluck the caterpillar off the plant and let it crawl across her fingers and up her arms. As it kept growing and growing and eating and eating, I decided to call on an expert for advice, just to make sure I wasn’t inadvertently harming the creature – or my daughter, for that matter.

Here’s what I learned:

  • Our caterpillar is a “woolly bear,” from the arctiidae family, said Jeffrey Miller, an entomologist at Oregon State University after I sent him a photo. It would grow into a moth, not a butterfly. To identify any caterpillar in the wild, get a copy of Caterpillars of Eastern North America, by David L. Wagner, an entomologist at the University of Connecticut, or go to his terrific U.S.-wide Web site. Miller has a detailed guide to Pacific Northwest caterpillars here.
  • Unlike many caterpillars, a woolly bear goes through a “wandering” stage just before weaving its cocoon, so Miller urged me to sequester it ASAP, which I did using a plastic Tupperware container topped with some gauze that I held in place with a rubber band. Eliza and I cleaned the container every day and gave it fresh begonia leaves, but no water, because, as Miller said, “they will drown themselves.”
  • Wild vs. kits. Kits are simpler, because everything’s already there for you. But, to me, catching a caterpillar in nature was much more fun. Miller also noted that butterflies born from kits would most likely not be native to the region where you live. "You don’t want to mix genes from different populations, because you don’t know the consequences,” he says. “For Monarch butterflies, the consequence would be confusion in how and where to migrate.” The tricky part of adopting a caterpillar from the wild will be figuring out what it likes to eat; in an ideal world, you’d find a baby caterpillar that is still on the leaf where it hatched. But the guides mentioned above should help with that as well.
  • To make caterpillar observation more fun for kids, Miller suggested observing two or more caterpillars at a time, and making a race out of which will weave its cocoon first. Keep one in a cool place, and one in a hot place to observe how warmer temperatures help them grow faster.

Here are some other entomology projects and events to look into. We might try these this summer as well.

Help Cornell University scientists track U.S. ladybug populations.

Join Nature’s Notebook, a national plant and animal phenology observation program in which Scientific American is a partner.

If you happen to live near Penn State University, they host an annual Great Insect Fair at their University Park campus. This year’s is on Sept. 17, 2011.

As for our project, about a week ago, the caterpillar wove a small hairy cocoon for itself against the gauze top of its plastic container. I feel as nervous as an expectant parent. Will it come out okay? When will it emerge? What will it look like? Stay tuned.

Do you have successful entomology projects to share, or other tips? Please leave a comment.