|Pipevine Swallowtail (Battus philenor) feeding on Southwestern Pipevine (Aristolochia watsonii)
|Southwestern Pipevine (Aristolochia watsonii) flower
Nevertheless, Pipevine Swallowtail caterpillars feed exclusively on plants in the genus Aristolochia. Besides occurring on our endemic vine they can also be found on a tropical relative that is cultivated at Tohono Chul Park.
The caterpillars themselves are not negatively impacted by the toxin. Their physiology is adapted to dealing with it. They sequester the toxin in their bodies and become poisonous and probably bad tasting themselves. Their aposematic colors, either red with lighter red appendages or black with red spikes (the occurrence of either morph seems to be temperature dependent) warns predators not to bother them. For a warning like this to be effective, the toxin should be unpleasant but not deadly so an inexperienced predator has a chance to learn by trial, the predator should be able to see colors and he needs to be smart enough to learn. This probably all applies to birds and reptiles and maybe small rodents like the grasshopper mouse..
|caterpillar with partly extended osmeterium (topright end)
|Mating Pipevine Swallowtails. Note that the female has only just emerged from the chrysalis that can be seen in the left bottom corner
|Red-spotted Purple Limenitis arthemis catterpillar and adults