Variation in pupation site preference is hypothesized to drive the evolution of environmentally cued pupal color dimorphism in swallowtail butterflies. Support for this hypothesis comes from comparisons of natural pupation sites of species monomorphic and dimorphic for pupal color. Here, we show that interspecific differences in pupation site preferences in nature are to a large extent mimicked in a controlled common garden experiment, suggesting that these differences are genetic. We gave larvae of three swallowtail species a choice of yellow and blue surfaces for pupation. Given the absorption spectra of green vegetation and the spectral sensitivities of the larval eyes, yellow and blue surfaces should be strong indicators of green and brown pupation sites, respectively. Papilio glaucus L., which produces only brown pupae and pupates near the ground in nature, chose to pupate near the bottom of the blue surfaces. In contrast, Battus philenor (L.) and Eurytides marcellus (Cramer), which produce dimorphic pupae, chose to pupate on both yellow and blue surfaces. B. philenor typically chose sites on blue surfaces that were significantly higher than were those of P. glaucus. We also found no differences between geographic populations of B. philenor. The distribution of pupation heights for E. marcellus was bimodal, possibly indicating a genetic polymorphism in pupation site preference. In a separate experiment, we asked whether rearing photoperiod affected pupation site preferences in Papilio polyxenes F. as suggested by observations in the field. Our results showed a clear effect, with larvae choosing only brown pupation sites when reared on an autumnal photoperiod.