Spicebush Swallowtail

The Spicebush Swallowtail is a member of the swallowtail family Papilionidae, found through much of the eastern United States wherever its namesake host plants, spicebush and sassafras, grow in forest understory. As an adult, it is a Batesian mimic of the chemically defended Pipevine Swallowtail, sharing a similar black body with an iridescent blue-green hindwing flush, which offers it some protection from predators despite lacking the toxins of its model.

The species is perhaps best known for its remarkable caterpillar, which in its later instars develops two large, cartoonish false eyespots on a swollen thorax, an adaptation thought to mimic a small snake and startle potential predators such as birds. Young caterpillars additionally resemble bird droppings, and all stages construct a folded-leaf shelter for daytime shelter.

As both pollinator and forest-understory herbivore, the Spicebush Swallowtail plays a role in the ecology of eastern deciduous woodlands, tightly linked to the Lauraceae family plants it depends on.

• Upperside is black with a row of pale cream-to-yellow spots along the forewing margin; hindwing shows a blue-green (males) or more blue (females) iridescent wash.
• Underside hindwing has two rows of orange spots and a pale blue-green area, distinguishing it from the true Pipevine Swallowtail it mimics.
• Wings are moderately broad with a single slender tail per hindwing.
• Distinguished from the Pipevine Swallowtail by the row of pale marginal spots on the upperside forewing (absent or faint in Pipevine) and from Black Swallowtail by lacking a distinct row of yellow spots across the entire wing.

Found throughout the eastern United States, from New England south to Florida and west to the Great Plains, generally within or near deciduous forest habitat.

Adults favor forest edges, wooded stream corridors, and shaded gardens where spicebush or sassafras grow in the understory, and are active from spring through early fall with multiple generations in the southern part of the range.

Adults nectar at a variety of woodland and garden flowers, including jewelweed, milkweed, and thistle, and males often patrol along forest edges and stream corridors searching for mates. Caterpillars feed on spicebush and sassafras leaves, folding a leaf edge over themselves with silk to create a protective daytime retreat, emerging at night to feed.

The caterpillar's swollen thorax with large false eyespots is a defensive display believed to deter predators by resembling a small snake when the leaf shelter is disturbed. The species is both a pollinator as an adult and a specialist herbivore of Lauraceae shrubs as a larva.

Females lay single pale green eggs on the underside of spicebush or sassafras leaves. Young caterpillars are dark and resemble bird droppings, while later instars turn green or yellow-green with large false eyespots on a swollen thorax, feeding within a folded-leaf shelter.

The chrysalis is mottled brown or green, attached to a twig or leaf litter. The species produces two generations per year across most of its range through complete metamorphosis, overwintering as a chrysalis.