Eastern Black Swallowtail
Papilo polyxenes

Photo by Bernell MacDonald from Pixabay
Summary
It might seem surprising, but black swallowtails were originally a wet meadow species, feeding on plants such as water parsnip and water hemlock. But as early as the 1820’s, draining and clearing of their habitat began to change the landscape, and the black swallowtail adapted to feed on non-native family members: meadow wildflowers such as Queen Anne’s lace (Daucus carota,) and cultivated garden plants like carrots, fennel, dill and parsley. All of these hosts (native or not) are members of the Apiaceae family, with which the swallowtail has co-evolved.
Female butterflies are lured to their host plants by a combination of chemical cues released from the plant, and they have chemoreceptors on their legs to help them find the right spot to lay eggs. Females drum their legs against the plant, releasing plant juices; chemoreceptors along the spines tell the butterfly whether she is standing on the correct host plant. And because they are in the same family, plants like dill and fennel “smell right” to swallowtails!
If you’d like to offer some native alternatives to your herb garden, golden Alexanders (Zizia aurea), rattlesnake master (Eryngium yuccafolium) and great angelica (Angelica atropupurea) are all fine choices for our area.
More Details
FAMILY
Papilionidae (Swallowtails)
IDENTIFICATION
Wingspan 2.71-3.30 inches; dorsal forewing with two rows of cream-colored spots, ventral forewing with two rows of yellow-orange spots.
HABITAT
Woodlands, fields, yards, gardens
LIFE CYCLE
Pale yellow eggs can be found on upper surface of a leaf, and also on the stems and flowers of the host plant. In earliest stages, the caterpillar has a white patch, called a saddle. When the caterpillar is ready to pupate, it hangs upright on a twig and spins a silk thread, or "girdle" around it's body. Overwintering generations exhibit a brown color. Adults: fan their wings when they feed.
HOST PLANTS
Larvae feed on species of the parsley and carrot family. (Apiaceae).
Ecosystem Connections
The caterpillars are herbivores that graze on vegetation, and the adults play a role in pollination. Its resemblance to the toxic pipevine swallowtail offers protection from predators. When it is raised on the deadly water hemlock (Cicuta douglasii), this species likely becomes truly toxic itself.