Analyses of two-dimensional chromatographic flavonoid patterns of butterflies reared on different grass species have shown that the flavonoid pattern ofMelanargia galathea is dependent on the flavonoid content of the larval diet. This confirms the dietary origin of flavonoid pigments inM. galathea. The flavonoid patterns of butterflies reared on different grass species differ from each other and from the larval food plants;M. galathea reared on the same grass species have identical flavonoid patterns. Differences in the butterfly and larval food plant flavonoid patterns indicate that the ingested flavonoids are metabolized byM. galathea or its gut flora before sequestration. The distinct flavonoid patterns of butterflies reared on different larval food plants have been defined as the flavonoid fingerprint profiles for each grass species. Similarity between theFestuca rubra flavonoid fingerprint profile and the constant flavonoid pattern characteristic of wild-capturedMelanargia suggests thatMelanargia larvae are not generalist grass feeders, but are specific toF. rubra or toF. rubra and a few closely related grass species in the wild.