Insect eggs are often characterized by an intricately sculptured external surface, which has been used to a limited extent as a taxonomic character, but not at all in comparisons among populations within a species or among populations of closely related species. We describe egg morphology by using scanning electron microscopy from 12 populations within a species complex of host-specific butterflies in the family Lycaenidae. Variation is found among populations and habitats. Adaptive hypotheses are discussed, and the observed variation is placed within the biogeographical context of the Sierra Nevada Mountains and adjacent regions.