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The Neotropical genus Heliconius (Nymphalidae) is unique among butterflies for its pollen-feeding behaviour. With the application of saliva, they extract amino acids from pollen grains on the outside of the proboscis. We predicted that the salivary glands of pollen-feeding Heliconiinae would show adaptations to this derived feeding behaviour. A biometrical analysis of the salivary glands revealed that pollen-feeding butterflies of the genus Heliconius have disproportionately longer and more voluminous salivary glands than nonpollen-feeding Nymphalidae. The first two components in the principal component analysis explained approximately 95% of the total variance. The size-dependent factor score coefficients of body length and salivary gland parameters were predominately represented on axis 1. They significantly discriminated pollen-feeding from nonpollen-feeding heliconiines on that axis. Factor score coefficients for the volume of the secretory region of the salivary glands separated heliconiines from the outgroup species. The detailed biometrical analysis of salivary glands features thus provides strong evidence that the secretory regions of the salivary glands are larger in pollen-feeding butterflies. We concluded that pollen feeding is associated with a high production of salivary fluid. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 97, 604–612. [ABSTRACT FROM AUTHOR]