I’ve battled bishop’s weed (Aegopodium podagraria) in my garden for 35 years.¹ As much as I detest it, (please don’t plant it), I’ve learned that what’s despised by one creature may mean survival to another. Bishop’s weed, a member of the parsley family, is one of a small number of host plants or “homes” for native black swallowtail butterfly caterpillars.²

A black swallowtail caterpillar (Papilio polyxenes) feasts on bishop’s weed, a member of the parsley family.

As I dug out the weeds a couple of weeks ago, I spotted a caterpillar with light blue-green and black stripes dotted with yellow. The clues to its identity were its location on a member of the parsley family, the only plant type that black swallowtails live on and eat, and the color and pattern of its stripes. (It looked similar to a monarch, but monarch caterpillars only eat milkweed and their stripes are yellow, black and white.) I searched through the rest of the bishop’s weed and found a second caterpillar. In May I’d seen an adult black swallowtail visiting the weed, where it must have deposited eggs.

Two rows of well-defined yellow spots help to distinguish the black swallowtail from other swallowtail species in our area.

Not a rare butterfly, but a handsome one, the black swallowtail (sometimes called the parsley swallowtail) is native to the eastern United States and Canada. Its body and wings are black with highlights of yellow, blue and orange. The tail ends in two narrow lobes that give it the common name of swallowtail. Two rows of bright yellow spots mark the wings. The hindwings are blue in the area between the yellow rows near the tail. Each hindwing ends in a circular reddish spot. The underside of each wing has rows of light yellow spots, with bands of orange separated by spatterings of blue. Females usually show more blue coloring and males usually have more yellow. The wing span is 3.5 – 4.5 inches, with the female generally larger than the male.

The undersides of the hindwings are marked with bright orange and a dusting of blue.

In the Upper Midwest, black swallowtails produce two generations of offspring between May and October. The second generation overwinters in a brown chrysalis until the following spring. The caterpillars in my garden probably hatched in May. Depending on weather conditions and host plant availability, the eggs hatch in three-to-nine days. The caterpillars eat and grow through five stages, or instars, as they increase in size and change in appearance, which may take up to 30 days. The mature caterpillar forms its chrysalis and molts one final time. The ones I saw will leave their chrysalises in two-to-three weeks as mature black swallowtails ready to produce the next generation. Adults nectar on clover, milkweed, thistle, bee balm and other perennials. Watch for them to be on the wing in July — and, consider growing one of the more well-behaved members of the parsley family, such as dill, carrot, parsley or sweet fennel, on which this lovely creature can live and dine!

¹Also known as goutweed and ground elder, this non-native member of the parsley family was imported and marketed as a fast-growing ground cover that was frequently planted with European buckthorn (Rhombus cathartica) and creeping bellflower (Campanula rapunculoides). There’s also a variegated form called snow-on-the-mountain. Over the years, we’ve had it chemically treated, dug out and the soil replaced, but it returned each time. Now, I just try to prevent it from spreading.

²Other members of the parsley family include carrot, dill, sweet fennel, Queen Anne’s lace and, of course, parsley.

Further Reading:

Butterflies and Moths of North America

Wisconsin Horticulture – UW-Madison

Weber, Larry. (2006). Butterflies of the North Woods. Duluth, Minnesota: Kollath & Stensaas Publishing.