This unusual-looking caterpillar is the larval form of the pipevine swallowtail butterfly.
This caterpillar is recognizable primarily by the “fleshy projections” which extend from its body. These projections, sometimes described as “tentacles,” occur on segments T1, T2, T3, and A2—that is to say, the first, second, third, and fifth segments. The projections on the first section are twice as long as those on any of the following segments. These caterpillars, which can reach 5.5 cm, are usually black. However, their coloration is affected by temperature; those experiencing warmer temperatures shift from black to smoky red colored. Most have red-orange dorsal warts on the abdomen.
Once the caterpillars have matured, they metamorphose into distinctive chrysalises. These, in turn, transform into the Pipevine Swallowtail Butterflies. They have a wing span of 7-13 cm. The fore-wing is coal-black above and gray below. Males’ hind wings are a brighter metallic blue than the females’, and the cream-colored spots which line the wing are smaller in males. In the north, B. philenor butterflies go through two generations in a year; in more southern habitats they exist in “continuous broods.” When a male butterfly has mated a female, she will lay clusters of orange-red, circular eggs on or under the leaves of pipevines.
This butterfly is named after the caterpillar’s primary food source. B. philenor caterpillars feed exclusively on plants in the genus Aristolochia, the pipevines. 
Pipevines are toxic to most animals; however, upon consumption, these caterpillars incorporate the toxins into their bodies and become toxic themselves. They remain toxic from the later caterpillar stages throughout their life. In fact, other butterflies have been shown to mimic B. philenor as a form of defense, because of B. philenor’s bad taste and toxicity to predators. The adults feed on the nectar of a wide variety of flowers.
The specimen on the stick is beginning to pupate. The active specimen was discovered on the pipevine in the Burns garden (see the large, partially eaten leaves and bud in the tank). Pipevines do not grow naturally at this elevation.
Hazel Galloway
Sources:
- http://animaldiversity.ummz.umich.edu/site/accounts/information/Battus_philenor.html
- Wagner, David L. Caterpillars of Eastern North America. Princeton: Princeton University Press, 2005.