1. 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.2. 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.3. In the natural treatment, butterflies classified as flower visitors were more efficient at feeding from the tubes, reaching an average 1.83× deeper into the tubes than the other species and never getting their proboscises stuck. The non-flowervisiting species, in contrast, had their proboscises remain in the tube 17× longer than the flower-visiting species, with 90% of them getting their proboscises at least partially stuck. The butterfly species with generalist feeding habits fed more efficiently than the non-flower visitors, but less than the flower visitors. A similar pattern was observed in the forced treatment. 4. Flower-visiting butterflies had smoother and more tapered proboscises, lower friction forces and a semi-circular cross-section that would reduce bendability and was augmented by a more sclerotized cuticle. Proboscises of flower-visiting butterflies, therefore, have a suite of adaptations that operate synergistically to optimize their feeding habits.

Fluid-feeding insects, such as butterflies, moths and flies (20% of all animal species), are faced with the common selection pressure of having to remove and feed on trace amounts of fluids from porous surfaces. Insects able to acquire fluids that are confined to pores during drought conditions would have an adaptive advantage and increased fitness over other individuals. Here, we performed feeding trials using solutions with magnetic nanoparticles to show that butterflies and flies have mouthparts adapted to pull liquids from porous surfaces using capillary action as the governing principle. In addition, the ability to feed on the liquids collected from pores depends on a relationship between the diameter of the mouthpart conduits and substrate pore size diameter; insects with mouthpart conduit diameters larger than the pores cannot successfully feed, thus there is a limiting substrate pore size from which each species can acquire liquids for fluid uptake. Given that natural selection independently favoured mouthpart architectures that support these methods of fluid uptake (Diptera and Lepidoptera share a common ancestor 280 Ma that had chewing mouthparts), we suggest that the convergence of this mechanism advocates this as an optimal strategy for pulling trace amounts of fluids from porous surfaces.

Few insect species are as popular as periodical cicadas (Magicicada spp.). Despite representing an enormous biomass and numbers that exceed 370/m2 during mass emergences, the extended time period of the underground nymphal stages (up to 17 years) complicates investigations of their life history traits and ecology. Upon emergence, female cicadas mate and then use their ovipositors to cut through wood to lay their eggs. Given the ability to penetrate into wood, we hypothesized that the ovipositor cuticle is augmented with inorganic elements, which could increase hardness and reduce ovipositor fracturing. We used scanning electron microscopy and energy dispersive x-ray spectroscopy to evaluate the material properties of ovipositors of four cicada species, including three species of periodical cicadas. We found 14 inorganic elements of the cuticle, of which P, Ca, Si, Mg, Na, Fe, Zn, Mn, Cl, K, and S show the highest concentrations (%wt) near the apex of the ovipositor, where other structural modifications for penetrating wood are present. To the best of our knowledge, this is the first report of metal deposits in the cuticle of true bugs (Hemiptera, >80,000 described species).

Antlion larvae are fluid-feeding ambush predators that feed on arthropods trapped in their funnel-shaped pits built in sandy habitats; however, details are lacking about their feeding mechanism. Here we tested the hypothesis that the antlion, Myrmeleon crudelis, has adaptations that facilitate fluid feeding in sandy habitats. We measured contact angles of water droplets and used the capillary-rise technique to assess mouthpart wettability. A structural organization was discovered that provides a hydrophobic-hydrophilic wetting dichotomy that would simultaneously support self-cleaning and fluid uptake and is enabled by antiparallel movements of the maxillae. The mouthparts also are augmented by their mechanical properties, including maxillae and mandible tips that might be heavily sclerotized, as determined by confocal microscopy, which likely facilitate piercing prey. Our findings provide insight on how antlion larvae have overcome the challenges of fluid feeding in sandy habitats, which likely contributed to their success and widespread distribution.