Patterns of intraspecific variation in the size of ventral wing spots were examined among populations of Speyeria idalia Drury. All morphological variables were significantly correlated with longitude but not latitude. Principal components and discriminant function analyses of the morphological data were also consistent with a longitudinal, clinal pattern of variation. Geographic variation in morphology was concordant with patterns of mitochondrial DNA, which showed fixed differences between eastern and western populations. Inclusion of samples from populations that are currently extinct in the center of the species’ range suggests clinal, rather than the currently observed discrete, variation was originally present. The appearance of discrete variation due to extinction in the center of a cline has previously been observed in the tiger beetle Cicindela dorsalis Say and may be more common than has previously been acknowledged. These results lend support the idea that conservation should attempt to preserve historical patterns of intraspecific variation rather than protect a limited number of individuals in a given species.