Proboscis adaptations for flower feeding

Butterflies use a proboscis, a microfluidic probe engineered by natural selection, to feed on nutritive fluids. The structural configuration of proboscises relates to feeding habits; however, the adaptations that enable proboscis entry into narrow floral corollas lack experimental evidence.
Here, we investigated proboscis adaptations that enable entry into corollas using funnel-shaped glass capillary tubes and performed feeding trials with six butterfly species of different feeding habits. Proboscises were either guided (natural treatment) or forced (forced treatment) into the capillary tubes that were filled with a 20% sucrose solution. The treatments were video recorded to determine the depth the proboscises reached into the tube and how long they remained there. The results were interpreted in terms of proboscis morphology, friction forces, and the material properties of the cuticle.
In the natural treatment, butterflies classified as flower visitors were more efficient at fee...