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Current biomechanical models suggest that butterflies and moths use their proboscis as a drinking straw pulling nectar as a continuous liquid column. Our analyses revealed an alternative mode for fluid uptake: drinking bubble trains that help defeat drag. We combined X-ray phase-contrast imaging, optical video microscopy, micro-computed tomography, phylogenetic models of evolution and fluid mechanics models of bubble-train formation to understand the biomechanics of butterfly and moth feeding. Our models suggest that the bubble-train mechanism appeared in the early evolution of butterflies and moths with a proboscis long enough to coil. We propose that, in addition to the ability to drink a continuous column of fluid from pools, the ability to exploit fluid films by capitalizing on bubble trains would have expanded the range of available food sources, facilitating diversification of Lepidoptera. 

To probe its environment, the flying insect controllably flexes, twists, and maneuvers its antennae by coupling mechanical deformations with the sensory output. We question how the materials properties of insect antennae could influence their performance. A comparative study was conducted on four hawkmoth species: Manduca sexta, Ceratomia catalpae, Manduca quinquemaculata, and Xylophanes tersa. The morphology of the antennae of three hawkmoths that hover while feeding and one putatively non-nectar-feeding hawkmoth (Ceratomia catalpa) do not fundamentally differ, and all the antennae are comb-like (i.e., pectinate), markedly in males but weakly in females. Applying different weights to the free end of extracted cantilevered antennae, we discovered anisotropy in flexural rigidity when the antenna is forced to bend dorsally versus ventrally. The flexural rigidity of male antennae was less than that of females. Compared with the hawkmoths that hover while feeding, Ceratomia catalpae has almost two orders of magnitude lower flexural rigidity. Tensile tests showed that the stiffness of male and female antennae is almost the same. Therefore, the differences in flexural rigidity are explained by the distinct shapes of the antennal pectination. Like bristles in a comb, the pectinations provide extra rigidity to the antenna. We discuss the biological implications of these discoveries in relation to the flight habits of hawkmoths. Flexural anisotropy of antennae is expected in other groups of insects, but the targeted outcome may differ. Our work offers promising new applications of shaped fibers as mechanical sensors. 

In insects vulnerable to dehydration, the mechanistic reaction of blood after wounding is rapid. It allows insects to minimize blood loss by sealing the wound and forming primary clots that provide scaffolding for the formation of new tissue. Using nano-rheological magnetic rotational spectroscopy with nickel nanorods and extensional rheology, we studied the properties of blood dripping from the wound of caterpillars of the Carolina sphinx moth (Manduca sexta) with a high concentration of blood cells. We discovered that wound sealing followed a two-step scenario. First, in a few seconds, the Newtonian low-viscosity blood turns into a non-Newtonian viscoelastic fluid that minimizes blood loss by retracting the dripping blood back into the wound. Next, blood cells aggregate, starting from the interfaces and propagating inward. We studied these processes using optical phase-contrast and polarized microscopy, X-ray imaging, and modeling. Comparative analyses of the cell-rich and cell-poor blood of different insects revealed common features of blood behavior. These discoveries can help design fast-working thickeners for vertebrate blood, including human blood. 

Hovering hawkmoths expend significant energy while feeding, which should select for greater feeding efficiency. Although increased feeding efficiency has been implicitly assumed, it has never been assessed. We hypothesized that hawkmoths have proboscises specialized for gathering nectar passively. Using contact angle and capillary pressure to evaluate capillary action of the proboscis, we conducted a comparative analysis of wetting and absorption properties for 13 species of hawkmoths. We showed that all 13 species have a hydrophilic proboscis. In contradistinction, the proboscises of all other tested lepidopteran species have a wetting dichotomy with only the distal ∼10% hydrophilic. Longer proboscises are more wettable, suggesting that species of hawkmoths with long proboscises are more efficient at acquiring nectar by the proboscis surface than are species with shorter proboscises. All hawkmoth species also show strong capillary pressures which, together with the feeding behaviors we observed, ensure that nectar will be delivered to the food canal efficiently. The patterns we found suggest that different subfamilies of hawkmoths use different feeding strategies. Our comparative approach reveals that hawkmoths are unique among Lepidoptera and highlights the importance of considering the physical characteristics of the proboscis to understand the evolution and diversification of hawkmoths. 

With the developments in nanotechnology, nanofibrous materials attract great attention as possible platforms for fluidic engineering. This requires an understanding of droplet interactions with fibers when gravity plays no significant role. This work aims to classify all possible axisymmetric configurations of droplets on fibers. The contact angle that the drop makes with the fiber surface is allowed to change from 0° to 180°. Nodoidal apple-like droplets with inverted menisci cusped toward the droplet center and unduloidal droplets with menisci cusped away from the droplet center were introduced and fully analyzed. The existing theory describing axisymmetric droplets on fibers is significantly enriched introducing new morphological configurations of droplets. It is experimentally shown that the barreled droplets could be formed on non-wettable fibers offering contact angles greater than 90°. The theory was quantitatively confirmed with hemispherical droplets formed at the end of a capillary tube and satisfying all the boundary conditions of the model. It is expected that the developed theory could be used for the design of nanofiber-based fluidic devices and for drop-on-demand technologies. 

Viscosity determines the resistance of haemolymph flow through the insect body. For flying insects, viscosity is a major physiological parameter limiting flight performance by controlling the flow rate of fuel to the flight muscles, circulating nutrients and rapidly removing metabolic waste products. The more viscous the haemolymph, the greater the metabolic energy needed to pump it through confined spaces. By employing magnetic rotational spectroscopy with nickel nanorods, we showed that viscosity of haemolymph in resting hawkmoths (Sphingidae) depends on wing size non-monotonically. Viscosity increases for small hawkmoths with high wingbeat frequencies, reaches a maximum for middle-sized hawkmoths with moderate wingbeat frequencies, and decreases in large hawkmoths with slower wingbeat frequencies but greater lift. Accordingly, hawkmoths with small and large wings have viscosities approaching that of water, whereas hawkmoths with mid-sized wings have more than twofold greater viscosity. The metabolic demands of flight correlate with significant changes in circulatory strategies via modulation of haemolymph viscosity. Thus, the evolution of hovering flight would require fine-tuned viscosity adjustments to balance the need for the haemolymph to carry more fuel to the flight muscles while decreasing the viscous dissipation associated with its circulation. 

Films formed by dip coating brass wires with dilute and semi-dilute solutions of polyvinyl butyral in benzyl alcohol were studied in their liquid and solid states. While dilute and semi-dilute solutions behaved as Maxwell viscoelastic fluids, the thickness of the liquid films followed the Landau-Levich-Derjaguin prediction for Newtonian fluids. At a very slow rate of coating, the film thickness was difficult to evaluate. Therefore, the dynamic contact angle was studied in detail. We discovered that polymer additives preserve the advancing contact angle at its static value while the receding contact angle follows the Cox–Voinov theory. In contrast, the thickness of solid films does not correlate with the Landau-Levich-Derjaguin predictions. Only solutions of high-molecular-weight polymers form smooth solid films. Solutions of low-molecular-weight polymers may form either solid films with an inhomogeneous roughness or solid polymer domains separated by the dry substrate. In technological applications, very dilute polymer solutions of high-molecular-weight polymers can be used to avoid inhomogeneities in solid films. These solutions form smooth solid films, and the film thickness can be controlled by the experimental coating conditions.