The Pipevine Swallowtail (Battus philenor)
By Kelly Rourke, Pollinator Partnership
It’s easy to confuse this striking butterfly with the black swallowtail (Papilo polyxen) as both species have dark forewings and you can find some black swallowtails that also wear iridescent blue on their hindwings. The black swallowtail comes into our gardens to lay eggs on carrots, dill, parsley and other members of the celery family. In contrast, the caterpillars of pipevines, sometimes referred to as blue swallowtails, eat only the leaves of birthworts and dutchman’s pipes (Aristolochia). If you want to lure these butterflies into your garden you should provide them with birthwort vines available at native plant nurseries. These woody vines are rather primitive and easy to grow if you have some dappled shade and add humus to your soil. They are related to magnolias, but in contrast, are native.
Pipevine swallowtails are found mostly in warm climates foraging in open woodlands and meadows. Their geographic distribution stretches across the southern half of the United States and continues towards the equator to southern Mexico.
Butterflies can be identified to species throughout their various developmental stages. Adult females lay clusters of eggs on or under pipevine leaves, usually exposed to the sun. Pipevine leaves are toxic to many vertebrate animals, and Battus philenor adopts this chemical characteristic from feeding off its host plant in the larval stage. This species is warningly colored, with its eggs red-orange and circular. The caterpillars are black with red projections and spots running down their backs, looking even less desirable to hungry predators. This coloration can be affected by temperature with warmer climates resulting in shades from black to red. Battus philenor’s chrysalis can be identified by looking at the posterior end which is segmented and has an inward curve. The ventral thorax is raised and the head has a pair of horns at the anterior dorsal (back) portion. This amazing butterfly seems to ward off predators even in its most defenseless state.
Battus philenor’s wingspan can stretch from 2 ¾ to 5 inches. The forewing of adult pipevine swallowtails is black on top and gray below. Sexual dimorphism is obvious in the dorsal hindwing. Males have smaller cream or pale spots compared to females, and their spots run along the fringe of the wings. Males are also a brighter metallic blue in the dorsal hindwing region. The bottom half of the ventral hindwing of both sexes is metallic blue. A single row of seven orange spots and small pale, cream dots are found at the edge of the wing embedded in the blue section. This is the pipevine swallowtail’s most identifiable characteristic.
Adult butterflies feed off of floral nectar and often visit a different set of plants than the leaf-eating caterpillars. Plants commonly visited include thistles, bergamot, lilac, viper’s bugloss, common azaleas, phlox, teasel, dame’s rocket, lantana, petunias, verbenas, lupines, yellow star thistle, California buckeye, yerba santa, broiaceas and hilias.