Featherwing beetles fly with style

Abstract

The aerial athleticism of insects is impressive on any scale, but the airborne feats of the miniature beetle Paratuposa placentis are particularly impressive considering their ultra-compact size. At roughly the size of a small amoeba – just 400 μm – their bodies house tiny muscles. Nevertheless, they fly as fast as insects that are 3 times their size. Led by Alexey Polilov at Lomonosov Moscow State University, Russia, researchers at institutions across the globe – including in Russia, Japan, Germany and Vietnam – set out to investigate what strategies these petite insects employ to keep themselves upright and aloft.Paratuposa placentis earned their nickname ‘featherwing beetles’ from their remarkable feathery wings. Instead of the membranous wings of their larger relatives, these beetles’ wings are made up of one thick spine with bristles growing out of it like a fringe. Wispy wings are lighter than membranous wings, but they don't produce as much aerodynamic force.To see how these distinctive wings allow the beetles to fly, the researchers captured high-speed videos of the insects in flight. The stunning videos provide a previously unseen glimpse into how flight is accomplished on such a small scale. They tracked the wing stroke paths by comparing wing positions across consecutive video frames. Like other insects, the beetles adjust the angle of their wings through each stroke so that the tips of their wings trace a figure-of-eight path. Unlike in larger insects, these beetles’ wings often touch each other at both the highest and lowest part of each wing stroke. This maneuver, called ‘clap-and-fling’ gives each wing stroke an extra aerodynamic boost.The team analyzed the wing paths and found that the unique wing stroke can be broken down into two half-strokes, each made up of a ‘power’ stroke that produces upward force and a ‘recovery’ stroke that stabilizes the animal. The power strokes create the aerodynamic force needed to keep the beetle in the air and the recovery strokes help the insect maintain balance. In addition to the wings, the beetles employ their hardened shell-like modified forewings, called elytra, to steady their flight. The elytra move in opposition to the wings, so that when the feathery wings are directed down, the elytra flap up and then down again as the wings swoop up. This antagonism stabilizes the beetle's body, so it doesn't somersault through the air.Despite the beetles’ miniscule size, they propel themselves through the air by employing unique wing stroke strategies. Their feathery wings and shell-like elytra flap in opposite directions to drive flight and steady the animal as it speeds through the air.