Wingtip folds and ripples on saturniid moths create decoy echoes against bat biosonar

Buckling-induced sound production in the aeroelastic tymbals of Yponomeuta

The loss of elastic stability (buckling) can lead to catastrophic failure in the context of traditional engineering structures. Conversely, in nature, buckling often serves a desirable function, such as in the prey-trapping mechanism of the Venus fly trap (Dionaea muscipula). This paper investigates the buckling-enabled sound production in the wingbeat-powered (aeroelastic) tymbals of Yponomeuta moths. The hindwings of Yponomeuta possess a striated band of ridges that snap through sequentially during the up- and downstroke of the wingbeat cycle-a process reminiscent of cellular buckling in compressed slender shells. As a result, bursts of ultrasonic clicks are produced that deter predators (i.e. bats). Using various biological and mechanical characterization techniques, we show that wing camber changes during the wingbeat cycle act as the single actuation mechanism that causes buckling to propagate sequentially through each stria on the tymbal. The snap-through of each stria excites a bald patch of the wing's membrane, thereby amplifying sound pressure levels and radiating sound at the resonant frequencies of the patch. In addition, the interaction of phased tymbal clicks from the two wings enhances the directivity of the acoustic signal strength, suggesting an improvement in acoustic protection. These findings unveil the acousto-mechanics of Yponomeuta tymbals and uncover their buckling-driven evolutionary origin. We anticipate that through bioinspiration, aeroelastic tymbals will encourage novel developments in the context of multi-stable morphing structures, acoustic structural monitoring, and soft robotics.

Contrasting laboratory and field outcomes of bat-moth interactions

Predator-prey interactions are important but difficult to study in the field. Therefore, laboratory studies are often used to examine the outcomes of predator-prey interactions. Previous laboratory studies have shown that moth hearing and ultrasound production can help prey avoid being eaten by bats. We report here that laboratory behavioural outcomes may not accurately reflect the outcomes of field bat-moth interactions. We tested the success rates of two bat species capturing moths with distinct anti-bat tactics using behavioural experiments. We compared the results with the dietary composition of field bats using next-generation DNA sequencing. Rhinolophus episcopus and Rhinolophus osgoodi had a lower rate of capture success when hunting for moths that produce anti-bat clicks than for silent eared moths and earless moths. Unexpectedly, the success rates of the bats capturing silent eared moths and earless moths did not differ significantly from each other. However, the field bats had a higher proportion of silent eared moths than that of earless moths and that of clicking moths in their diets. The difference between the proportions of silent eared moths and earless moths in the bat diets can be explained by the difference between their abundance in bat foraging habitats. These findings suggest that moth defensive tactics, bat countertactics and moth availability collectively shape the diets of insectivorous bats. This study illustrates the importance of using a combination of behavioural experiments and molecular genetic techniques to reveal the complex interactions between predators and prey in nature.

Moth wings as sound absorber metasurface

In noise control applications, a perfect metasurface absorber would have the desirable traits of not only mitigating unwanted sound, but also being much thinner than the wavelengths of interest. Such deep-subwavelength performance is difficult to achieve technologically, yet moth wings, as natural metamaterials, offer functionality as efficient sound absorbers through the action of the numerous resonant scales that decorate their wing membrane. Here, we quantify the potential for moth wings to act as a sound-absorbing metasurface coating for acoustically reflective substrates. Moth wings were found to be efficient sound absorbers, reducing reflection from an acoustically hard surface by up to 87% at the lowest frequency tested (20 kHz), despite a thickness to wavelength ratio of up to 1/50. Remarkably, after the removal of the scales from the dorsal surface the wing's orientation on the surface changed its absorptive performance: absorption remains high when the bald wing membrane faces the sound but breaks down almost completely in the reverse orientation. Numerical simulations confirm the strong influence of the air gap below the wing membrane but only when it is adorned with scales. The finding that moth wings act as deep-subwavelength sound-absorbing metasurfaces opens the door to bioinspired, high-performance sound mitigation solutions.

Hidden phylogenomic signal helps elucidate arsenurine silkmoth phylogeny and the evolution of body size and wing shape trade-offs

One of the key objectives in biological research is understanding how evolutionary processes have produced Earth's diversity. A critical step towards revealing these processes is an investigation of evolutionary tradeoffs - that is, the opposing pressures of multiple selective forces. For millennia, nocturnal moths have had to balance successful flight, as they search for mates or host plants, with evading bat predators. However, the potential for evolutionary trade-offs between wing shape and body size are poorly understood. In this study, we used phylogenomics and geometric morphometrics to examine the evolution of wing shape in the wild silkmoth subfamily Arsenurinae (Saturniidae) and evaluate potential evolutionary relationships between body size and wing shape. The phylogeny was inferred based on 782 loci from target capture data of 42 arsenurine species representing all 10 recognized genera. After detecting in our data one of the most vexing problems in phylogenetic inference - a region of a tree that possesses short branches and no "support" for relationships (i.e., a polytomy), we looked for hidden phylogenomic signal (i.e., inspecting differing phylogenetic inferences, alternative support values, quartets, and phylogenetic networks) to better illuminate the most probable generic relationships within the subfamily. We found there are putative evolutionary trade-offs between wing shape, body size, and the interaction of fore- and hindwing shape. Namely, body size tends to decrease with increasing hindwing length but increases as forewing shape becomes more complex. Additionally, the type of hindwing (i.e., tail or no tail) a lineage possesses has a significant effect on the complexity of forewing shape. We outline possible selective forces driving the complex hindwing shapes that make Arsenurinae, and silkmoths as a whole, so charismatic.