The following article originally appeared in Butterfly Gardener (Vol 11: No.4, Winter 2006).
Host Plant: Aristolochia
By Lenora Larson
Gardeners are continually beset by difficult choices of the “you can’t have your cake and eat it too” variety. Some of these mutually exclusive choices are fairly benign: “Should I cut that flower for a bouquet, or leave it to glory the garden?” Others are more momentous: “Should I leave that tree, or cut it to create a sunny butterfly garden?” And some are gut-wrenching: Should I leave the Pipevine Swallowtail caterpillars or rescue the delicate baby vine?”
When I turned to butterfly gardening in 1991, the beauty of the Pipevine Swallowtail motivated me to yearn for its obligate host, Aristolochia. Of course I’d never seen the butterfly in person, only in the pages of books. But the range showed Eastern Kansas and I believed the adage, “plant it and they will come.”
I finally found Aristolochea macrophyllla in the White Flower Farm catalog and ordered it for an early spring planting. It languished for a few months, then died in the Kansas heat and humidity. The next year, same story. The third try, another failure. But the fourth try succeeded and the vine made it through a killer Kansas winter. Slowly, pitifully, it began to climb its trellis, unaware of the catalog description of “vigorous vine quickly spreading to 30 feet.” By the sixth year of attempting Aristolochia, it was starting to flourish and I saw my first female Pipevine Swallowtail. She was a glorious creature with sooty black forewings and shimmering azure hindwings edged with a neat row of creamy spots. There was no mistaking her intentions as she wagged her abdomen towards the leaves of my vine. I watched with delight as she planted a cluster of the rusty brown eggs along a leaf petiole.
My delight turned to despair. Unlike most butterfly caterpillars, PVC’s move in herds, devouring all the tender new growth and leaving ragged holes in the mature leaves. I chose caterpillars and my struggling vine was stripped bare. But the caterpillars made it all worthwhile. They quickly became my favorites with their velvety maroon bodies adorned with orange bumps. And those fleshy bristles constantly quiver with excitement. Just darling!
Pipevine Swallowtails had found me, but it wouldn’t be for long if I couldn’t consistently provide an ample supply of Pipevine foliage. Fortunately, I found a mail order source for the Midwestern native Pipevine, A. tomentosa. I ordered six vines from the Missouri Wildflower Nursery.
All survived the transplanting and began their climb to glory in soil augmented with well-rotted manure to hold moisture. The vines grow upwards with a twisting pattern and are adorned by large heart-shaped leaves that are slightly fuzzy or ‘tomentose.” The flowers, the “Dutchman’s Pipe,” are the typical pipe-shaped olive blooms, more curious than beautiful. The vines are so vigorous, that even large herds of caterpillars do not harm them. And I welcome the ragged holes as clues to check for my friends.
Gray’s Manual of Botany tells us that Aristolochiaceae is in the Birthwort family, along with our native Ginger, Asarum. By the doctrine of signatures, they are reputed to be of value in childbirth because the curved flower looks like a human fetus in the womb. To my eyes, Pipevine is a more accurate name. The Aristolochea contain the poisonous aristolochic acid, a renal toxin and probable carcinogen. But the caterpillars are immune and gratefully accept the toxicity as they feed. Imitation is the best compliment and several other species of adult swallowtails mimic the coloration of the Pipevine Swallowtail to take advantage of predators’ learned distaste.
Worldwide, there are over 500 members of the Aristolochia family and the HortiPlex database lists 30 Pipevines for cultivation. Native choices flourish throughout most of the United States. Aristolochea serpentaria, Virginia Snakeroot; A. reticulata, the Texas Snakeroot and A. californica announce their provenance by name. In Eastern US, A. macrophylla grows in moist shaded woodlands. We Midwesterners find A. tomentosa from zone 5 to 8. New England and Ontario have A. clematitis , and I’ve spotted A. watsonii with tiny leaves and hungry Pipevine caterpillars in the Arizona desert. If you are lucky enough to live in zone 8 and above, you can grow the obscenely beautiful tropical Pipevines such as A. elegans, A. clittoralis, and A. grandiflora. with florid pinks and purples adorning the huge blossoms; however, there are reports that caterpillars dining on these tropicals soon die rather than flourish.
What about that first A. macrophylla? It did recover and limped along for another two years with occasional foliar predations by the Pipevine Caterpillars. It finally succumbed to a fungal disease. In the meantime, the natives have triumphed in two separate locations: three are covering a fence in full sun, and three climb a pergola in partial shade.
What have we learned about choices? By choosing native Pipevines who have co-evolved with the butterfly in their habitat, the butterfly gardener can indeed have their cake and eat it too.