Overview
The Black Swallowtail (Papilio polyxenes), also celebrated across North America as the eastern black swallowtail or parsnip swallowtail and honored as the official state butterfly of Oklahoma, is one of the most prominent, elegant, and beloved butterflies on the continent. Adorned with velvety jet-black wings bordered by dual bands of gleaming golden-yellow spots and delicate tails resembling the fork of a swallow, this iconic member of the family Papilionidae is a familiar and welcome visitor to sunlit flower gardens, wild carrot meadows, and rural roadsides throughout summer.
AT A GLANCE
- Common Name: Black Swallowtail
- Scientific Name: Papilio polyxenes
- Category: Invertebrates
- Subcategory: Insects
- Size: Wingspan 6.5 to 11 cm (2.6 to 4.3 in); females slightly larger than males
- Weight: 0.4 to 0.9 g
- Lifespan: Adult stage lasts 10 to 14 days; overwintering chrysalis phase lasts up to 9 months
- Diet: Adults: Nectar from red clover, milkweed, thistles, and zinnias; Larvae: Foliage of Apiaceae family plants including wild carrot, parsley, dill, fennel, and celery
- Habitat: Open fields, sunny meadows, prairies, pastures, roadsides, agricultural margins, and suburban vegetable and flower gardens
- Range: North America (Eastern and Central North America from southern Canada throughout the United States to northern Mexico, west to the Rocky Mountains)
- Conservation Status: Least Concern
Ecologically, Papilio polyxenes serves as a vital generalist pollinator and an exquisite classic model of Batesian mimicry. The adult female black swallowtail exhibits reduced yellow spotting and an expansive splash of shimmering metallic cobalt-blue on her hindwings, closely mimicking the distasteful and toxic pipevine swallowtail (Battus philenor) to deter predatory birds. Its voracious, handsomely ringed black-and-green striped caterpillars, known widely to vegetable gardeners as ‘parsley worms’, sequester aromatic chemical compounds from host plants in the carrot family (Apiaceae), utilizing them in an astonishing chemical defense display.
Biology and Physical Characteristics
The morphology of Papilio polyxenes reflects sophisticated adaptations for rapid aerodynamic flight, thermal absorption, and chemical defense. The wings are predominantly black, which allows the butterfly to rapidly absorb solar radiation on cool mornings by basking with wings spread perpendicular to the sun’s rays. Sexual dimorphism is pronounced: males exhibit a bold, bright submarginal band of large yellow spots across both fore- and hindwings, while females display smaller, paler yellow spots accented by an expansive, iridescent iridescent blue cloud across the lower hindwing. Each hindwing terminates in a slender, spatulate tail and features a prominent orange-and-black anal eyespot that diverts avian strikes away from the vital head and body.
Behavior and Ecology
Adult male black swallowtails exhibit classic ‘hilltopping’ behavior: during sunny afternoons, males congregate atop prominent hilltops, ridges, or tall trees, competing in acrobatic aerial spiral dogfights to establish and defend lookout territories where they intercept receptive females. When threatened, the caterpillars deploy one of the most astonishing defense mechanisms in the insect world: an eversible, bifurcated orange gland called the ‘osmeterium’ that pops out from immediately behind the head like fleshy snake horns, exuding a pungent, rancid odor rich in isobutyric and 2-methylbutyric acids that drives away predatory ants and birds.
Conservation and Human Impact
Papilio polyxenes is categorized as Least Concern by the IUCN, maintaining abundant, widespread populations across its native North American range. Because its caterpillars thrive on common agricultural weeds like Queen Anne’s lace (Daucus carota) as well as popular garden culinary herbs like parsley, dill, and fennel, the species has benefited substantially from human agricultural and suburban expansion. Primary local threats include broad-spectrum mosquito fogging, garden insecticide spraying, and the clearing of native meadow corridors.
Interesting Factoid
When attacked, the black swallowtail caterpillar suddenly shoots out a pair of bright orange, horn-like fleshy tentacles from behind its head called an osmeterium, releasing a foul, rancid smell resembling rotten butter to repel predators.