Written By David Greene
To the right is a pipevine swallowtail caterpillar (Battus philenor). No doubt that you have probably seen dozens of the butterflies that these bad boys become. Swallowtail butterflies are some of the largest and most common butterflies found here in the Southern Appalachian Mountains.
Let me point out a few neat things about this picture that might not be obvious at first glance. The plant that this caterpillar is on is a dutchman’s pipevine (Aristolochia macrophylla). This vine is pretty common, grows like crazy, has big ol’ heart shaped leaves (hence the species name: macro = big and phylla = leaf), and its flowers are pretty weird. The flowers look kind of like a pipe, a tobacco pipe, one that perhaps a Dutchman would smoke.
Most butterflies are host specific, meaning that a species of butterfly may have one specific species of plant that they always lay their eggs on. For the pipevine swallowtail, their host is the dutchman’s pipevine.
The ductchman’s pipevine is toxic, and very few animals can eat it. However, the pipevine swallowtail has evolved to not only be able to eat the pipevine without harm, but they can also store the toxic chemicals within their own bodies. This adaptation makes the swallowtails toxic to would-be predators. This adaptation is so successful that many other swallowtail species mimic the adult pipevine swallowtail to avoid predation.
Another neat defense mechanism can be seen in the picture above with what looks like a yellow, forked tongue coming from what appears to be the caterpillar’s mouth. That is an osmeterium, which is found in all caterpillars belonging to the swallowtail family. When the caterpillar feels threatened, the osmeterium protrudes from the prothorax (segment just behind the head) and secretes volatile organic compounds. These compounds ward off predators such as ants, spiders, and mantis.
What lesson can we learn from the pipevine swallowtail? Well, whether you are looking at a caterpillar on a leaf, or some fungus on a log, there is far more to the situation than meets the eye. The natural world is an endlessly fascinating and intricate place. Take some time to visit your nearest wilderness area, and see for yourself.