Attract and identify a black swallowtail butterfly

Black Swallowtail Butterfly Facts

• Common name: Black swallowtail butterfly
• Wingspan: 2 3/4 to 3 1/4 inches
• Distinctive Markings: Primarily black from above, males have an extra band of yellow dots. Their bodies are also black with rows of yellow dots. On hindwings, blue markings and black-centered orange eyespots
• Habitat: Open areas such as gardens or wetlands
• Caterpillar: Bright green with black bands and yellow or orange dots. The youngest caterpillars are nearly all black with a white back patch and orange spots
• Host Plants: Celery, dill, parsley, sweet fennel and caraway
• Backyard Favorites: Adults sip nectar from red clover, zinnia and thistle

Eggs and Host Plants

I saw my first black swallowtail butterfly the other day, and it immediately sent me running to my parsley bed to see if the butterfly had laid any eggs. You see, most people grow herbs for cooking, but I tend to grow them mostly as host plants for butterflies.

Black swallowtail butterflies (Papilio polyxenes) lay eggs on celery, sweet fennel, caraway, parsley and dill, along with common roadside wildflowers like Queen Anne’s lace. This is one of the easiest butterflies to lure to your own backyard, just by planting a bed of these herbs in a sunny spot. The eggs are lovely little yellow orbs, very easy to spot on the herb leaves.

Discover fascinating swallowtail butterfly facts.

What Do Black Swallowtail Caterpillars Look Like?

The eggs hatch into tiny black caterpillars with a white stripe across the middle. As they grow, the caterpillars become mostly green with black bands and yellow markings. Some people call them parsley caterpillars.

The caterpillars of this species undergo many changes before they’re ready to pupate. These different phases are called “instars.” The process takes about two weeks from egg to chrysalis.

Black Swallowtail Caterpillars in Winter

A black swallowtail spends the winter as a chrysalis (remember, butterflies form a chrysalis, while moths form a cocoon). It contains a chemical that acts as antifreeze so it can survive cold temps. Then it emerges as an adult come spring, and it’s always worth the wait.

“I raised black swallowtails this year. Seven caterpillars have remained chrysalises. How do I store them so that they become butterflies in the spring?” asks Birds & Blooms reader Teresa Savage of Canton, Michigan.

Kenn and Kimberly Kaufman say, “It’s normal for a black swallowtail to spend the winter in the chrysalis stage, then emerge as an adult in spring. The chrysalis contains chemicals that act as antifreeze so it can survive cold temperatures. It’s best to keep it in outdoorsy conditions, not in a warm house. We recommend someplace like an unheated garage or a screened-in porch. Place the chrysalis inside a container that protects it from mice or other animals, with ventilation for free airflow. The container should be large enough that the adult has room to spread its wings when it emerges.”

“Where do the black swallowtail caterpillars on my dill plants spend their winter?” asks reader Vicki Brown of Omaha, Nebraska.

Kenn and Kimberly say, “We applaud you for sharing your dill with the caterpillars. It’s wonderful to watch the life cycle of butterflies—and host plants are a vital part of the process. It seems hard to believe that something so small and delicate could survive the winter, but the last generation of black swallowtails from late summer or fall will overwinter in the chrysalis stage, emerging as adults in spring. The chrysalis, looking a little like a rolled-up leaf, is usually attached to a vertical stem of a plant.”

Where to Find Black Swallowtail Butterflies

Black swallowtails are found throughout much of the U.S., including east of the Rocky Mountains and parts of the Southwest. They closely resemble a common Southeastern species, the spicebush swallowtail. Although they fly all summer long, in the deep south the herbs they use as host plants may struggle to grow in the summer heat. Try keeping the herbs in partial shade and watering frequently to keep them alive and encourage black swallowtails to visit.