Pipevine Swallowtail vs Polydamas Swallowtail

The pipevines growing in the MOSI Outside gardens support two species of butterflies: Pipevine Swallowtails (Battus philenor) and Polydamas Swallowtail (Battus polydamas). Here's a look at the similarities and differences between these species throughout their life cycle.

Egg

Though both species lay their eggs on pipevines (Aristolochia spp) in a similar cluster pattern, these eggs are easily told apart by color. Pipevine ST eggs are red, while Polydamas ST eggs are yellow or greenish-yellow.

Pipevine Swallowtail Eggs (top) and Polydamas Swallowtail Eggs (bottom)

Larva (Caterpillar)

In the first instar, these caterpillars can be difficult to tell apart, but as they grow some obvious differences begin to appear. Pipevine ST larvae have much longer tubercles toward the front of their bodies, and move much more quickly. Polydamas ST found in the wild are likely to have a striped pattern, while those raised in captivity and not exposed to UV light are darker in color and more similar to the Pipevine ST.

Pipevine Swallowtail Larva (left), and Polydamas Swallowtail Larvae (right). Note that the far right Polydamas Swallowtail  larva, which was raised in captivity, is darker in color than the one to its left, which was found in the wild.

Pupa (Chrysalis)

In this stage, the two species are nearly impossible to tell apart. Both have color variations from green to brown, with yellow-orange markings. There are some slight differences in size and color, and experienced lepidopterists can usually pinpoint them correctly, but can't necessarily explain how they know. At this point, about the only way to know which species is which is to wait! 

In this photo, the Polydamas Swallowtail pupa is on the left, and the Pipevine Swallowtail pupa is on the right.

Butterfly

In their final adult stage, these two butterflies have only superficial similarities. Both are dark, and of similar size. But here the similarities end. Polydamas Swallowtails don't actually even have the "tails" at the bottoms of their wings that other swallowtails are known for. They do have distinctive yellow markings along their lower wings, giving them the other common name "Gold Rim Swallowtail". Pipevine Swallowtails are a uniform dark color when seen from the top, but males flash an iridescent blue when their wings catch the sunlight.

Pipevine Swallowtail (top); Polydamas Swallowtail (bottom)

Even with their wings closed, these butterflies aren't too difficult to tell apart because of the difference in silhouette. Polydamas Swallowtails have more red on their underwings, while Pipevines show orange and blue. Even their bodies are different, with Pipevines having white spots and Polydamas red/orange ones.

Pipevine Swallowtail (top); Polydamas Swallowtail (bottom)

One final fact worth noting regards the host plants used by these butterflies. Though both feed on plants in the Aristolochia family, we have found that some non-native species of pipevine can be toxic to Pipevine Swallowtails, though Polydamas Swallowtails do fine with them. Specifically, we have found Aristolochia gigantea, A. littoralis (syn. A. elegans), and A. grandiflora to be toxic to Pipevine larvae. Learn more about pipevines here.