Illinois Natural History Survey - University of Illinois

Species Spotlight: Zebra Swallowtail

If a contest were held to pick the most beautiful butterfly in Illinois, the zebra swallowtail would likely make the final four and perhaps win the coveted title. Zebra swallowtails occur in Illinois from about midway in the state to the southern tip. These inhabitants of moist, shaded woods, however, are far more common in the south. Zebra swallowtails are polymorphic, that is, they have different forms and markings depending on the season. Each spring, small brightly colored examples gracefully dart through sun-dappled woods. The larger and less colorful summer form may be seen just about anytime during the summer season. Zebra swallowtails are not large, as swallowtails go, and have a wingspan of 2.5-4.5 inches. This delicate species is black or dark brown with bright white stripes and a bright red spot at the base. A daggerlike tail graces each hind wing.

When viewed on a pin with wings spread, likely in a budding entomologist's collection, the species appears quite gaudily colored. In its native habitat, though, it is often very difficult to detect because its color pattern helps it elude predators. The same can be said about real zebras in Africa; their color patterns also help to break up their outlines and make them difficult for lions to detect. The zebra swallowtail's black and white stripes blend in remarkably well with the backgrounds present in a sunny woods, and the red spot at the base of its long tails gives predators a false head to aim at, one far removed from the insect's actual head. This increases the swallowtail's chances of surviving a bird attack by 50%.

Zebra swallowtail, Eurytides marcellus.

Adults are nectar feeders and can be seen flitting about on woodland flowers. Adults may also puddle club together--small congregations of zebras often settle on a moist spot in the forest and imbibe nitrogen left by a passing animal. Not only does puddle clubbing help zebras with their nutrition, but the clumps of colorful butterflies, almost always bachelor males, also attract the attention of a passing female.

Zebra swallowtail caterpillars feed on only one species of plant, the leaves of pawpaw, a common understory tree in many Illinois woodlands. Females appear in the forest 2 to 3 weeks before the pawpaw trees leaf out. Once the plants leaf out, the female begins to lay pea-green, spherical eggs on the upper surface of the leaves. The eggs hatch in 7-8 days. The caterpillar is pale green with yellow and black bands across its body. After 3 weeks the caterpillar is fully grown and approximately 2 inches long.

While Illinois' zebras may not be quite as large as their African counterparts, they are every bit as showy, in their own diminutive way, and form a fascinating component of Illinois woodlands.

Susan Post, Center for Economic Entomology

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