The form and function of the mouthparts in adult Lepidoptera and their feeding behavior are reviewed from evolutionary and ecological points of view. The formation of the suctorial proboscis encompasses a fluid-tight food tube, special linking structures, modified sensory equipment, and novel intrinsic musculature. The evolution of these functionally important traits can be reconstructed within the Lepidoptera. The proboscis movements are explained by a hydraulic mechanism for uncoiling, whereas recoiling is governed by the intrinsic proboscis musculature and the cuticular elasticity. Fluid uptake is accomplished by the action of the cranial sucking pump, which enables uptake of a wide range of fluid quantities from different food sources. Nectar-feeding species exhibit stereotypical proboscis movements during flower handling. Behavioral modifications and derived proboscis morphology are often associated with specialized feeding preferences or an obligatory switch to alternative food sources.

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Many species of nymphalid butter¯ies only exceptionally visit¯owers and feed instead on tree sap, juice of rotting fruits and other decaying substances. To investigate whether the proboscis morphology of these non-¯ower-visiting Nymphalidae differs from that of nectarivorous butter¯ies, representatives from 64 nymphalid species with known feeding preferences were examined. Morphometric comparison of the proboscis revealed characteristic differences in proboscis length, tip-region length, wall composition, and number and shape of proboscis sensilla between these two feeding guilds. The investigated non-¯ower-visiting species belonging to Apaturinae, Limenitidinae, Morphinae, Brassolinae, Nymphalinae and Satyrinae, possess a relatively short and light-coloured proboscis which has a long tip-region with a great number of club-shaped sensilla styloconica. Densely arranged, these sensilla form a¯at brush located laterally from the openings into the food canal on the dorsal side of the tip-region. Among the non-¯ower-visiting species, a second type of proboscis was found in fruit-feeding Charaxinae the stout tip-region of which is equipped with more widely spaced sensilla styloconica. The investigated¯ower-visiting Heliconiinae, Nymphalinae, Satyrinae, Danainae and Ithomiinae are characterized by a slender, darker-coloured proboscis with a rather short tip-region bearing fewer sensilla styloconica in a loose arrangement. Discriminant analysis revealed that the tip-region length, the number of sensilla styloconica and the relative proboscis length are the most important discriminating variables between the¯ower-visiting and the nonower-visiting species. The proboscis morphology of nymphalid butter¯ies corresponds with certain feeding habits and allow us to make predictions on their food preferences. The`brush-tipped' proboscis seems to have a functional role in the accumulation of¯uid and the uptake of liquid from wet surfaces such as rotting fruits or tree sap. We conclude from the phylogeny of the examined taxa that this derived proboscis tip morphology evolved several times independently as an adaptation to the exploitation of new food resources.