Pipevine swallowtail (May 31, 2013)

The larva is easy to recognize, or some might say hard to forget. Two pipevine swallowtail caterpillars were submitted this week from Texas. The scientific name of this insect is Battus philenor, which has a nice ring to it and sounds like it could be a character on Downton Abbey.  The larvae look a bit dangerous and actually are, at least if one intends to eat them. Larvae feed on members of the plant genus Aristolochia, more commonly known as pipevines or birthworts which contain aristolochic acid, a toxic compound known to be a carcinogen and toxic to kidneys. There are actually several species of swallowtail butterflies that feed on Aristolochia and they accumulate aristolochic acid in their bodies. While it might seem that this would be harmful to the swallowtails it is actually good because, while the insects are not affected, things that eat the insects can be made sick. A predator of a larva that contains aristolochic acid is far less likely to make that mistake again and thus forego dining on further swallowtail larvae that use this form of chemical defense. The other thing about this species is that, while the larvae may be on the ugly side (a subjective statement to be sure), the adults are strikingly beautiful. I don't have a photo of the adults, but here is a link to the butterfly photos on Bugguide

Pipevine swallowtail larva. Photo credit: Rebecca Saxon.