Convergent evolution of a dichotomy in wettability on the mouthparts of flies and butterflies

Lepidoptera and Diptera, the premiere fluid feeders among insects, independently evolved mouthparts specialized for liquid uptake, i.e., an adaptation not shared by their common ancestor approximately 260-280 mya. Both groups face a common obstacle when feeding – they must be able to acquire fluids from flowers and other wetted surfaces while keeping their mouthparts clean of debris. Using contact angle measurements acquired with a capillary rise technique, the lepidopteran proboscis was previously shown to have an overall hydrophobic proximate region and a hydrophilic distal region, which relates to proboscis architecture. We employed a similar technique here to study the proboscises of three species of flies along previously unstudied lepidopteran species and found that they too possess a functionally defined drinking and nondrinking region. Using scanning electron microscopy, we show that butterflies and flies independently evolved similar strategies to have mouthparts with hydrophilic parts needed for feeding on fluids and hydrophobic parts with self-cleaning abilities.