September, 2008

Polydamas Swallowtail

What looks like a horned devil is actually the caterpillar of a swallowtail butterfly. The polydamas (Battus polydamas) is a rather uncommon species in our area because it is mainly tropical. The protrusions sticking out all over the body are very fleshy, and the whole insect has the consistency of one of those fake rubbery worms used by fishermen. The larvae are very selective in their diet and will only feed on pipevines in the genus Aristolochia. These plants are toxic and their chemicals give the caterpillars and subsequent adult butterflies protection from predators by making them unpalatable. There is actually another Battus species in our area, the much more common pipevine swallowtail. True to its name, that one feeds on pipevines as well. It tends, however, to prefer its pipevines to be a bit on the milder side. Common species that serve the pipevine swallowtail are our native swan flower (Aristolochia erecta) and the cultivated pipevine, Aristolochia fimbriata. While the polydamas caterpillars will feed on Aristolochia fimbriata too, they seem to prefer a more toxic diet, which comes in the form of Aristolochia elegans, known as the calico flower. This vine is tropical but does okay in our area, and we've had a plant growing for a number of years. Although it has not yet gotten large enough to produce the stunning flowers for which it is admired, the vine has increased each year to the point of finally attracting a female polydamas butterfly which then laid eggs. The caterpillars ate the entire vine. That will not hurt the plant, as it is adapted for this kind of assault and has a very thick root which stores enough nutrients to allow it to grow back.

The adult polydamas butterflies are often not recognized as swallowtails, as they lack the signature "tails" on their hind wings. They are also sometimes called "gold rims" because of the bright yellow dotted markings outlining their black wings.