Fairyflies are the tiniest insects on the planet: with body lengths averaging no more than a millimetre, the minute creatures barely get noticed. However, if you were to take a closer look, you would discover that the diminutive mini-beasts also sport extraordinary fringed wings. Explaining that the lengthy bristles that line the edge of the wing could play various roles – from reducing the weight of the wing to sensing air flow – Shannon Jones and Laura Miller from the University of North Carolina at Chapel Hill, USA, decided to test the possible impact of the bristles on fairyfly flight.
Working with Jones and Miller, Young Yun and Tyson Hedrick analysed the size and distribution of the bristles around the edges of the wings of 23 different species, ranging from the minute Kikiki huna to the heftier Eustochus nipponicus, and found that the tinier insects had the most tightly packed and slender bristles, in contrast to the larger species whose bristles were sparser and chunkier. The team also noticed that the bristles made up a larger portion of the wing's surface area in the smallest flies which they say, ‘supports the idea that bristles may play an important physiological or mechanical role for the smallest insects’.
Intrigued by the impact of the bristles on flight, Jones and Boyce Griffith calculated how the wings interacted with flowing air when tilted at various angles. They discovered that when the bristly wings were hardly tilted relative to the air flow, the wing produced as much force as a solid wing of the same size: the bristles may help the flies to reduce the weight of the wing without losing too much power. And when the team analysed the amount of force required to tear the wings apart when they meet together at the top of a wing beat – known as the clap and fling – they discovered that less force is required to prise bristly wings apart. They say, ‘These results support the idea that bristles may offer an aerodynamic benefit during clap and fling in tiny insects’, although they add that the bristles may also offer other benefits.