Hunting For Swallowtail Caterpillars In The Garden

I love it when science shows up. I especially love it when it appears in the school’s raised beds in the form of a swallowtail caterpillar, plump and lime green, maybe striped, maybe “staring” at me and the students with two big round “eyes” designed to scare the predators.

In this part of Northern Virginia, the spring science curriculum focuses on the monarch. I’ve never understood this because we live marginally on the monarch’s spring migration path, if at all. Swallowtails, though — we have those permanent residents in abundance. More than 550 species of swallowtail exist worldwide, but at our elementary school we primarily see Eastern black swallowtails, spicebush swallowtails, and tiger swallowtails (Virginia’s state insect).

The tigers are most obvious in the butterfly form, when they’re feeding on the nectar of perennials like purple coneflower (Echinacea purpurea). The caterpillars are harder to find, given that their primary local host is our tallest tree, the tulip tree (Liriodendron tulipifera). The spicebush caterpillars can also be tricky because they prefer to feed at night. During the day, as they settle on their spicebush (Lindera benzoin) or sassafras (Sassafras albidum) leaves, they spin a silk mat that shrinks as it dries, curling the leaves around them. We have found them in our sassafras seedlings, rolled up and resting.

What shows up in the greatest numbers on our grounds are Eastern black swallowtails. This is because one of our kindergarten teachers is a dill fanatic and a dedicated, hands-on educator. Her students are among the most active gardeners at our school, taking good care of two 4′ x 8′ raised beds. Dill and little else occupies one of them.

Swallowtail Caterpillars

The Eastern black caterpillars are also known as parsley caterpillars because they eat exclusively in the parsley family, which is comprised of some of the tastiest and most aromatic edibles: anise, coriander, cumin, fennel and, of course, dill and parsley. It also includes celery and carrots.

We first spied the caterpillars in the dill bed last week, and now our dill — or at least those stems that haven’t been chewed to nubs — is hanging heavy with plump, yellow-black-and-lime caterpillars.

We’re keeping a close eye on them, watching for when one maneuvers to a sturdier stem, hangs upright, and begins to spin silk threads around its body. The resulting chrysalis may be bright green and yellow or may be dull brown and tan. (Here’s a great time-lapse video of the life cycle.) When the butterfly emerges, it’ll have plenty of nectar sources to choose from: two of its favorites are common milkweed and orange butterfly weed (both are milkweeds). We planted both for our monarch caterpillars, which are being well taken care of inside the school by our second graders.

Here are a couple of tips for introducing your students to swallowtail caterpillars:

Avoid handling. They don’t like it. If you try to pick up an Eastern black swallowtail, what look like antennae will pop out of the top of its head. These are orange scent glands, and they can emit a stink if the caterpillar feels threatened.

Take advantage of the opportunity to teach your students about host plants. Caterpillars are notoriously selective eaters, and the sooner the kids learn this, the more swallowtails that will survive. Teach them that the females have laid their eggs on these specific plants because only this is what the just-born and developing caterpillars can eat. There’s no point moving the swallowtail to milkweed or mint or something else because it can’t and won’t eat it.

Look for molting caterpillars. Caterpillars spend about two weeks doing nothing but eating, eating, eating, and their skin can’t keep up with their quickly growing bodies. They will molt and grow into a new, often entirely different-looking, skin. The stages of growth are called instars, and some caterpillars have as many as five of them. If you see a caterpillar that isn’t moving or looks like a stuffed sausage, don’t touch it — it’s probably getting ready to molt and it’s more vulnerable to injury and stress at this point. You’d think it’d be fun to look for molted skin, but you won’t have much luck: Eastern black caterpillars eat their old skins.

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About the Author

With the endless passion for organic living, I - Ann Sanders has come up with the idea of creating A Green Hand. Being the founder and editor of A Green Hand, my goal is to provide everyone with a wide range of tips about healthy lifestyle with multiform categories including gardening, health & beauty, food recipe,...

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