While visiting the Cataloochee Valley of Great Smoky Mountains National Park in North Carolina last week, my wife and I came across a large number of pipevine swallowtails (Lepidoptera: Papilionidae: Battus philenor). These recently-deceased insects were all gathered around a small, dried-up puddle along a gravel road. I suspect they had been sucking up moisture or minerals from the mud and were run over by cars, or simply died of old age after mating.
These butterflies are found from the southern United States through southern Mexico where the larvae feed predominantly on their namesake pipevines (Aristolochia spp., Aristolochiaceae). It’s thought that these insects ingest toxic metabolites from their host plants (including aristolochic acid) and exhibit their own resulting toxicity to potential predators with their bright warning coloration.