This study documents the existence of a food plant related palatability spectrum in Florida queen butterflies (Danaus gilippus). Abdomens of butterflies reared on four asclepiad food plants differed significantly in cardenolide content and palatability to a generalist avian predator (Red—winged Blackbird). However, unpalatability did not directly parallel food plant or butterfly cardenolide content. Queens reared on Sarcostemma clausum were cardenolide free and essentially palatable (85% eaten). Butterflies reared on Asclepias tuberosa and A. incarnata were also virtually cardenolide free, but were weakly and moderately unpalatable, respectively (62 and 46% eaten). Queens reared on the high cardenolide Asclepias curassavica contained 101—753 mg cardenolide and were very unpalatable (8% eaten). This results suggest that in addition to cardenolides, other asclepiad phytochemicals are directly or indirectly utilized by queens as components of their systemic chemical defense. The demonstrated variation in queen palatability is predicted to affect the aversive conditioning of predators and thus the outcome of queen—predator encounters. Queen populations feeding on more than one asclepiad species must exhibit automimicry, with attack rates on individual butterflies dependent upon both the proportion of palatable automimics and the noxiousness of unpalatable automodels in the population. The verification of a queen palatability spectrum also contributes to understanding the dynamics of mimicry between queens and viceroy butterflies (Limenitis archippus). This study predicts that, as a consequence of regional differences in asclepiad floras, the viceroy queen mimicry relationship in Florida switches between the Batesian and Mullerian mimicry modes. In the extreme, queens feeding on certain food plants may be Batesian mimics of sympatric, moderately unpalatable viceroys, reversing the traditionally cited mimicry roles of these butterflies.