FROM THE GROUND UP: ‘Pet’ plant turns into kitchen science project

This black swallowtail caterpillar just molted, leaving its skin behind.
This black swallowtail caterpillar just molted, leaving its skin behind. PHOTO BY PAMELA BAXTER

Quite unexpectedly, I have a new pet, one that appeared on my doorstep just a week or so before Memorial Day. It’s easily been seven years since there were any animals in the house, so I’ve gotten out of practice in including pet care in my travel plans. Suddenly, here I was — barely two weeks into the venture — looking forward going away for the long holiday weekend.

What to do? I made sure that my pet had enough food to last the three days and drove off to my beach adventure. Don’t worry; I’m not an irresponsible pet owner. I knew that both my pet and my house would be fine. That’s because this new “pet” isn’t so much a pet as a creature that I’ve adopted.

Several weeks ago I discovered a rue plant growing between the paving stones on the front walkway, grown from seed that had dropped from the parent plant in the perennial border. When I tugged on it, the plant came out roots and all, so I put it in a glass of water on the kitchen counter until I had time to re-plant it somewhere else. In no time, two-and-a-half weeks went by. That’s when I noticed something different about the plant: on one of the leafy stems there was a tiny caterpillar, maybe half an inch long.

I recognized the caterpillar as the fledgling larva of the black swallowtail butterfly. There must have been an egg on the plant when I brought it in. I kept a close eye on the caterpillar; mostly to make sure that it was not, literally, eating itself out of house and home.

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In the process of making sure that the caterpillar had enough food, I found myself fascinated by the nearly constant changes that this tiny creature was going through: eat, rest, molt, eat its own discarded skin, and repeat. I was also amazed at how quickly it was growing.

Before going away for the weekend, I thought about transferring the caterpillar to the parent rue plant outside. Then I remembered last spring, when twelve black swallowtail caterpillars on that plant disappeared, one after another. I figured that they had been picked off and eaten by birds. I decided to keep this one safe indoors.

To be sure the caterpillar would have enough food to last, I cut a few extra stems of rue and added them to the jar. When I arrived back home, I found that there were plenty of leaves left. And the caterpillar was twice its previous size.

I thought, “Is this the perfect ‘pet’?” What other creature could be left alone for an unlimited amount of time, without worry? At the very least, it couldn’t get loose; by necessity, it was confined to that plant.

Which brings me to a larger discussion: in planning a garden, it’s important — and easy — to include plants that host both the larval and adult forms of insect pollinators. Recently, Monarch butterflies have become the “poster children” of threatened insect pollinators. More people are now aware that monarch larvae feed solely on milkweed plants and feel inspired to plant milkweed. But what about the other butterflies? What do they need?

Besides rue, black swallowtail butterflies look primarily for members of the parsley family — dill, parsley, carrots, celery, fennel, parsnips — to deposit their eggs. The hatched larvae can eat only the leaves of these plants, explains Erin Gettler in Bird Watcher’s Digest book, “Butterflies Backyard Guide.”

The swallowtail butterflies will sip nectar from many different flowers, including thistles, milkweed, purple coneflower, zinnias, Joe-Pye weed, privet, and wild bergamot, according to http://www.thebutterflysite.com/butterfly-food.shtml0.

Note: Butterfly bush (Buddleia davidii) is often listed as a good nectar source, but this non-native plant is invasive and there are plenty of other flowers that are more attractive. For some alternates, see http://bit.ly/2rcmZux. (Butterfly “weed” is a completely different plant, related to milkweed.)

Pam Baxter is an avid organic vegetable gardener who lives in Kimberton. Direct e-mail to pamelacbaxter@gmail.com, or send mail to P.O. Box 80, Kimberton, PA 19442. Join the conversation at “Chester County Roots,” a Facebook page for gardeners in the Delaware Valley. Go to Facebook, search for Chester County Roots, and “like” the page. To receive notice of updates, click or hover on “Liked” to set your preferences.