Wettability of the butterfly proboscis

Fluid-feeding insects have mouthparts composed of hydrophobic chitin, but are able to drink water, nectar, and aqueous nutrients. We used the butterfly proboscis to elucidate the structural and chemical adaptations necessary for fluid acquisition with a primarily hydrophobic natural device. Using a capillary-rise technique, we studied the wettability of the proboscis at a macroscale and characterized a drinking (hydrophilic) and a nondrinking region (hydrophobic). Structural examination at the hydrophilic and hydrophobic boundary revealed a set of adaptations that facilitate liquid entry into the hydrophilic food canal for uptake to the gut. Our study provides the first experimental confirmation of the wettability of insect mouthparts and reveals the natural solution for devices with fluid-feeding and self-cleaning abilities.