Spicebush Swallowtail Caterpillar

The spicebush swallowtail caterpillar is the larva of a common woodland butterfly found throughout much of the eastern United States, named for one of its primary host plants, spicebush. Like several other swallowtail larvae, it uses eyespot mimicry to deter predators, but it takes the strategy further by building a distinctive folded-leaf retreat that it occupies during the day.

Over its development the caterpillar changes color dramatically, shifting from an early dark and white pattern to a bright yellow-green form and finally to a more subdued orange-yellow before pupation, tracking changes that help it blend with both green and senescing foliage.

• Later instars are bright yellow-green to blue-green with a swollen, rounded thorax
• Two large yellow-orange eyespots with black pupils sit atop the thorax, each ringed with black
• A row of small blue dots often lines the sides near the rear of the body
• Younger caterpillars are dark brown and white, resembling bird droppings
• Body is smooth and hairless
• Distinguished from the similar tiger swallowtail caterpillar by its host plant (spicebush or sassafras) and slightly more elongated eyespots

This species is found across the eastern United States, from the Gulf Coast north into New England and the Midwest, wherever its host plants grow in forest understories, woodland edges, and shaded thickets. Caterpillars are most commonly found from late spring through early fall on spicebush and sassafras shrubs.

The caterpillar folds a leaf over itself with silk threads to create a tent-like shelter, resting inside during daylight hours and venturing out to feed mostly at night. This behavior, combined with its snake-like eyespots, helps it avoid detection and startle potential predators such as birds. It feeds exclusively on spicebush, sassafras, and occasionally related plants, and like other swallowtails it can evert a scent-releasing osmeterium gland when disturbed. As both caterpillar and adult butterfly, it plays a role in forest food webs and pollination.

Females lay pale round eggs singly on the underside of host leaves. The larva develops through five instars over several weeks, shifting in color from a bird-dropping mimic to the bright green eyespotted form and finally to a duller orange hue before pupating. It forms a chrysalis that can be green or brown depending on its surroundings, attached to a stem or leaf litter by a silk girdle. The species overwinters as a chrysalis in cooler climates, with one to three generations annually depending on latitude.