Support Swallowtail Butterflies With This Vine

Text by Caleb Melchior for the May/June 2019 issue of Horticulture.

In 2016 and 2017, my corner of the Internet was brightened by the delightful story of Tim Wong, a young scientist who devotes his off time to restoring the California pipevine swallowtail to San Francisco’s parks and gardens. Following his efforts, pipevine swallowtail populations in the city boomed. People called him “the butterfly whisperer.” How did he do it? He just kept planting regionally appropriate pipevines.

Pipevine (Aristolochia) is a genus of mostly vining plants found throughout the world. They contain aristolochic acid, a toxin that certain butterfly species and their larvae store in their bodies, making them unpalatable and even dangerous to predators.

In the eastern half of the United States, two native vining species are most widely planted to support swallowtails: the bigleaf pipevine (A. macrophylla; Zones 4–8) and woolly pipevine (A. tomentosa; Zones 5–8). Both are large, vigorous vines with attractive heart-shape foliage. Bigleaf pipevine, in particular, has elegant 12-inch (or larger) leaves that it holds densely, like overlapping shingles, on thick, winding vines. The flowers are small, two-inch pipes with a weird brown flare at the end. They nestle behind the foliage. Woolly pipevine is similar, but with smaller foliage and stems coated in a soft fuzz. Its flowers remain small, but they boast a yellow flare surrounding a chocolate-lipsticked trumpet flower.

These pipevines are dense and quick to grow, so make sure to have a substantial support structure in place before planting them. They grow best in soils high in organic matter, with regular moisture and good drainage. In the northern part of their range, they can tolerate full sun, but partial shade helps in hot-summer regions.

In the Southwest and California, plant California pipevine (A. californica; Zones 8–10). It’s more wiry than the eastern North American species, and its flowers have red veining. Throughout the continental United States, it’s generally advised to avoid planting elegant dutchman’s pipe (A. littoralis) and giant pelican flower (A. gigantea), both native to Brazil, in areas frequented by pipevine swallowtails, because the butterfly larvae can’t properly process the levels of aristolochic acid carried in these species’ leaves.

Besides planting regionally appropriate pipevines, how can you become a butterfly whisperer? Learn to identify different species of swallowtails. Pipevine swallowtails (Battusphilenor) are easy to distinguish from other North American swallowtails because when viewed from above (what butterfly experts call the “dorsal view”), they don’t have the heavy stained-glass effect of yellow or white flecks surrounded by heavy black veins that you see in other swallowtail species. Instead, the upper sides of their wings shade from dusy black on the forewings to a radiant blue on the hindwings. There may be a few silver spots, but they won’t be heavily bordered or veined in black. This color pattern makes the pipevine swallowtail easy to identify. The California subspecies B. p. hirsuta has smaller adults with hairier bodies.

Eggs are small, bright orange in color and laid on the stems of host plants. Larvae look like little two-inch-long sea slugs; they’re brown with protruding tubercules along the length of the body, each tipped with an orange dot. Pipevines are this species’ only larval food, so if you see a little brown caterpillar munching on your plants you should soon be the proud protector of your own flurry of spectacular black and blue pipevine swallowtails.

Image credit: Getty Images