Abstract
Flight speed is positively correlated with body size in animals1. However, miniature featherwing beetles can fly at speeds and accelerations of insects three times their size2. Here we show that this performance results from a reduced wing mass and a previously unknown type of wing-motion cycle. Our experiment combines three-dimensional reconstructions of morphology and kinematics in one of the smallest insects, the beetle Paratuposa placentis (body length 395 μm). The flapping bristled wings follow a pronounced figure-of-eight loop that consists of subperpendicular up and down strokes followed by claps at stroke reversals above and below the body. The elytra act as inertial brakes that prevent excessive body oscillation. Computational analyses suggest functional decomposition of the wingbeat cycle into two power half strokes, which produce a large upward force, and two down-dragging recovery half strokes. In contrast to heavier membranous wings, the motion of bristled wings of the same size requires little inertial power. Muscle mechanical power requirements thus remain positive throughout the wingbeat cycle, making elastic energy storage obsolete. These adaptations help to explain how extremely small insects have preserved good aerial performance during miniaturization, one of the factors of their evolutionary success.
Highlights
Large insects generally fly faster than smaller ones[1]
The increased angle of attack (AoA) during power strokes and the presence of recovery strokes are similar to the kinematics of swimming in miniature aquatic crustaceans (Supplementary Information), which move at similar flow regimes—for example, larvae of Artemia sp.[20], with a Reynolds number of 10
The findings reported here expand our understanding of the flight mechanics at low Reynolds numbers
Summary
The findings reported here expand our understanding of the flight mechanics at low Reynolds numbers. Small insects need to produce forces to support their body weight in conditions of high viscous drag on the body and wings. In P. placentis, these mechanisms improve the temporal distribution of muscle mechanical power requirements and help to maintain aerial performance at an extremely small body size If this flight style is common for miniature beetles, it may largely explain their worldwide abundance. 9. Santhanakrishnan, A. et al Clap and fling mechanism with interacting porous wings in tiny insect flight. Very small insects use novel wing flapping and drag principle to generate the weight-supporting vertical force. Kolomenskiy, D. et al Aerodynamic performance of a bristled wing of a very small insect: dynamically scaled model experiments and computational fluid dynamics simulations using a revolving wing model. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/
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