Papilio troilus
A large black swallowtail butterfly whose larvae feed exclusively on Lauraceae host plants, primarily sassafras and spicebush. Reaches the northern limit of its range in southern Ontario. Notable for its remarkable larval mimicry — caterpillars resemble bird droppings in early instars and green snakes in later instars.
Seasonal Activity
Diet
Sassafras and spicebush foliage (larva); nectar from Joe-Pye weed, jewelweed, honeysuckle, milkweeds, thistles, and dogbane (adult)
Lifecycle
Three generations per year throughout most of its range. Eggs are laid singly on the leaves of Lauraceae host plants. Early-instar larvae are brown and white, resembling bird droppings. Late-instar larvae are green with large false eyespots on the thorax, mimicking a green snake. When threatened, larvae evert a bright red osmeterium (Y-shaped organ) that resembles a snake's tongue. Pupae are brown (overwintering) or green (summer), attached to the underside of a leaf. The entire development cycle from egg to adult takes approximately one month.
Ecology
Native Habitats
Details
Description
The Spicebush Swallowtail (Papilio troilus) is a large, primarily black swallowtail butterfly with a wingspan of 7.6-10.2 cm. Males have a distinctive green-blue half-moon splotch on the hindwings, while females display a brighter blue patch. Both sexes have cream-coloured oval spots along the forewing margins and a bright orange spot at the base of the wings. The underside of the hindwing features a double row of orange spots, distinguishing it from the similar pipevine swallowtail. Adults fly low and fast through shaded woodlands, unlike most swallowtails which fly higher.
The species is ranked Secure (G5) globally by NatureServe. The nominate subspecies P. t. troilus ranges throughout the eastern United States and reaches its northern limit in southern Ontario, where it is a Carolinian zone specialist. This butterfly is the state butterfly of Mississippi.
Lifecycle
Spicebush Swallowtails produce three generations per year across most of their range. Females are highly selective, using chemoreceptors on their forelegs to identify Lauraceae host plants before ovipositing. Eggs are greenish-white, laid singly on host leaves.
The larval stage features one of the most elaborate mimicry displays in North American Lepidoptera. Early-instar caterpillars are dark brown with a white saddle, closely resembling bird droppings. By the fourth instar, larvae turn yellow-green with two large black-and-white false eyespots on a swollen thorax, creating a convincing snake mimic. When disturbed, the caterpillar everts a bright red, forked osmeterium that resembles a snake tongue, and rears up its head — completing an effective deterrent display.
Pupation occurs on the underside of a leaf near the ground. The pupa exhibits seasonal polyphenism: brown in winter (matching leafless branches) and green in summer. Adults emerge from overwintered pupae in spring, with flight periods extending from May through September in Ontario. Adults live 2 days to 2 weeks, feeding on nectar and engaging in mud-puddling behaviour at stream banks and moist soil.
Ecology
Larvae are obligate feeders on the Lauraceae family, with sassafras (Sassafras albidum) and spicebush (Lindera benzoin) as the primary hosts. This dietary specialization is so rigid that larvae will starve rather than feed on non-Lauraceae plants. The species feeds more efficiently on Lauraceae than any other Lepidoptera, a product of close co-evolutionary specialization.
Adults nectar on a wide variety of flowers, with preferences for Joe-Pye weed, jewelweed, honeysuckle, milkweeds, thistles, azalea, and dogbane. Both sexes engage in mud-puddling to obtain minerals. The species employs Batesian mimicry as adults — their resemblance to the toxic pipevine swallowtail (Battus philenor) deters avian predators. Males can thermoregulate effectively, allowing flight and feeding at cooler temperatures than many other butterflies.
Host Plants
Larvae feed exclusively on members of the Lauraceae family:
- Sassafras (Sassafras albidum) — primary host, preferred for oviposition
- Spicebush (Lindera benzoin) — primary host, namesake of the butterfly
- Tulip Tree (Liriodendron tulipifera), Sweetbay (Magnolia virginiana), and Prickly Ash (Zanthoxylum) are occasional alternate hosts
Habitat
In Ontario, the Spicebush Swallowtail is restricted to the Carolinian Forest zone of the extreme southwest, where its Lauraceae host plants occur. It inhabits deciduous woodlands, forest edges, and woody swamps. Males are typically found in moist, shaded woodland interiors, while females frequent more open, sunlit areas near host plants.
The broader North American range extends from southern Ontario and New England south to Florida and west to Texas and the Great Plains. The species occasionally strays as far as Manitoba, Colorado, and Cuba.