Beneficial aerodynamic effect of wing scales on the climbing flight of butterflies

Abstract

It is hypothesized that butterfly wing scale geometry and surface patterning may function to improve aerodynamic efficiency. In order to investigate this hypothesis, a method to measure butterfly flapping kinematics optically over long uninhibited flapping sequences was developed. Statistical results for the climbing flight flapping kinematics of 11 butterflies, based on a total of 236 individual flights, both with and without their wing scales, are presented. Results show, that for each of the 11 butterflies, the mean climbing efficiency decreased after scales were removed. Data was reduced to a single set of differences of climbing efficiency using are paired t-test. Results show a mean decrease in climbing efficiency of 32.2% occurred with a 95% confidence interval of 45.6%-18.8%. Similar analysis showed that the flapping amplitude decreased by 7% while the flapping frequency did not show a significant difference. Results provide strong evidence that butterfly wing scale geometry and surface patterning improve butterfly climbing efficiency. The authors hypothesize that the wing scale's effect in measured climbing efficiency may be due to an improved aerodynamic efficiency of the butterfly and could similarly be used on flapping wing micro air vehicles to potentially achieve similar gains in efficiency.

On the multifunctionality of butterfly scales: a scaling law for the ridges of cover scales

“…33 Although the above mentioned studies strongly suggest that buttery scales support the ight of butteries, it is an oen reported observation that butteries can still y without scales. 28 Nonetheless, the overall structure of the ridges and the observed ratio limit of 0.5 remind us of the famous study of Bechert et al 34 who studied the drag of a ribbed surface inspired by shark scales. Searching for an optimized design for these 'riblets', the authors found that a ratio of 0.5 between height and distance is optimal.…”

“…In general, it is reported that buttery scales, in addition to colouring, assist in thermoregulation, 11,12,25 escape from spider webs, 26 aerodynamics, 10,27,28 and wet self-cleaning. 8,29 Among these, aerodynamics and wet self-cleaning are the only features which rely mainly on the microstructure of the surface, i.e., the geometry of the upper lamina.…”

“…26 The scales are only loosely bound to the wing membrane and can be easily released (for comparative experiments for example). 10,19,28 The microstructure of the upper lamina has practically no effect on this. Thermoregulation in buttery wings, however, is in most cases a complex phenomenon where the combination of pigmentation as well as the micro-and nanostructure in the scales is important.…”

“…He reported an improvement in li of about 15% for wings with scales. Slegers et al 28 analysed the ight of living butteries utilizing high-speed cameras. Comparing the ight performance of butteries with and without scales, they observed that scales improve the climbing efficiency of butteries.…”

Hydrophobicity in clearwing Lepidoptera: impact of scale micro and nanostructure, and trade-off with optical transparency

“…They are characterized by wings entirely covered with flat and coloured lamellar scales (17). Through their pigmentation and structure, scales are involved in multiple functions such as antipredator defences (e. g. camouflage, deflection, mimicry in 18,19), communication (20), thermoregulation (17,(21)(22)(23), or flight enhancement (24,25). They also confer superhydrophobic properties to the wing, resulting in water repellency and self-cleaning (26,27).…”