Meet the Pollinators: The Swallowtail Butterfly

By Jill Eisenstein

Who doesn’t love the sight of butterflies in the summer garden? They flutter and glide, rise and dip like flowers in the wind. While they are more important and efficient pollinators in tropical regions, butterflies have nonetheless won our Northern hearts with their grace and beauty. They land on a flower, unfurl their long tongues to drink nectar, then move unhurriedly to another flower, sometimes quite far away. Though they lack specialized body parts for collecting pollen, they do transfer a little on their long legs and long tongues, and because they travel such distances, that can be important for cross-pollination and genetic diversity.

Perhaps none catch our attention quite like the large, brightly-colored swallowtails. Their family, Papilionidae, includes more than 550 species, but fewer than 30 live in North America. Most of them feature tails on their hind wings which resemble the tails of the swallow family of birds – hence their name.

Around here, the ones we are most likely to see are Eastern Tiger (Papilio glaucus), Black (Papilio polyxenes), Spicebush (Papilio troilus) and Giant (Papilio cresphontes) swallowtails. Less frequently, people have reported seeing Pipevine (Battus philenor) and Zebra (Protographium marcellus), seen more often in southern states.

But where are the swallowtails right now?

Swallowtail butterflies have gone through one generation over the summer and the caterpillars of the second generation of the year have finished their fifth instar (growth stage), found a branch, leaf litter, or a plant stem, and pupated into a casing called a chrysalis. Black swallowtails sometimes attach their chrysalises to sticks or rocks, usually quite close to the ground. There, in a dormant state – diapause – all of them resemble dead leaves. This is why many conservationists, such as those from the nonprofit Xerces Society for Invertebrate Conservation, encourage us to “leave the leaves” in fall; destroying leaves may destroy swallowtail butterfly chrysalises, as well as those of other invertebrates.

The pupae stop developing in the winter. Like some of the other animals living through sub-zero temperatures, they produce two compounds, glycerol and trehalose, to protect them from freezing. When the days begin to lengthen and the temperatures warm in spring, the pupae emerge as adult butterflies, mate, and begin laying eggs on plants. The larvae can eat right from hatching (“host plants”). Eastern tiger swallowtail larvae can feed on various host plants, including wild cherry, basswood, birch, ash, cottonwood, American mountain ash, and willow. Black swallowtail larvae are often known as “parsley caterpillars” since that’s one of their most common host plants. They also feed on dill, fennel, Queen Anne’s lace, and common rue. Giant swallowtails lay eggs on citrus trees, prickly ash and common rue. As the name suggests, the Spicebush swallowtail larvae feed on Spicebush, but also camphor, sweet bay, and tulip tree.

The eggs hatch in about 10 days and the caterpillars (larvae) stage lasts three to four weeks. As adults, swallowtail butterflies only live one to two weeks. The first generation in spring nectars on apple blossoms, wild cherry and lilac flowers. The second generation, the summer swallowtails, nectars on plants such as milkweed and Joe Pye Weed.

A diversity of native plants attracts a wider range of colorful swallowtails. Enjoy the swallowtail butterflies from spring to fall, and leave them some dead leaves to get through the winter in your yard and garden!