Dragonfly wings are thin and light and have a corrugated-like structure. There are lots of tiny cells between numerous veins and cross veins, which together form a stiff, yet relatively flexible structure which is able to bear alternating wing loads during the flight. Some veins are stiffer than others, particularly those at or near the leading edge, but also some of the cross veins. This gives the wing a unique combination of stiffness and flexibility. Dragonflies are remarkable fliers, and there have been many detailed investigations of their aerodynamic abilities; I have just dipped my toes into what is a voluminous literature.
A large dragonfly can reach a top speed of somewhere between 36 and 54 km/h (22 to 34 mph), and they are also highly maneuverable. Their cruising speed is probably closer to 12 or so km/hr, beating their wings about about 30 times per second. They are remarkably agile aerial predators, able to adjust their flight, and change direction, at any speed (including hovering).
The basic wing pattern of dragonflies has remained remarkably constant over geological time, which suggests that once this particular model had evolved, it was retained (or remained a conserved feature) for hundreds of millions of years. The Protodonata, the ancestors of modern dragonflies (Odonata), were flying in the Carboniferous, so they have had plenty of time to perfect their aerial abilities! They were also a lot larger than modern day dragonflies, so the wings would appear to work well on a larger scale!
All dragonfly wings have two noticeable features: a nodus and a stigma (see below). The pterostigma, to give it its full name, is a hollow structure on the leading edge of the wing. As well as being a pigmented spot – which may play a role in communication – it also has a significant effect on the aerodynamics of the wing. According to a study by R. Åke Norberg Norberg (at the University of Göteborg, in Sweden), because it is a slightly heavier part of the wing – but still only only 0.1 % of the total weight – it has a marked effect on the gliding ability of the dragonfly, enabling it to glide at speeds, 10–25% faster, in one species. It makes me wonder whether it is solid cuticle?
Due to its mass contribution and favourable location, the pterostigma tends to raise these speed limits by causing favourable, inertial, pitching moments during the acceleration phases of wing flapping. (Norberg, 1972).The nodus (above) – a stress-absorbing strip of soft cuticle – is an important feature, which allows a certain degree of wing twisting. It is a sort of one-way hinge which enables the dragonfly to deform – alter the shape – of the wings and thereby adjust their aerodynamic properties during flight. In both dragonfly and damselfly wings, the compound resilin – a rubberlike protein – is present in this and other vein joints, allowing twisting movements of the wings but preventing excess bending.
We tend to take it for granted that dragonflies are remarkable fliers, fast and highly maneuverable; but when one considers that they have been honing their abilities for such an unimaginably long period of time – before there were any mammals and before most flowering plants had evolved! – it is rather incredible. They have come up with, and perfected, a remarkable structure – a corrugated wing membrane – which we are only just beginning to fully understand (and copy).
Azuma, A., & Watanabe, T. (1988). Flight performance of a dragonfly. Journal of experimental biology, 137(1), 221-252.
Gorb, S. N. (1999). Serial elastic elements in the damselfly wing: mobile vein joints contain resilin. Naturwissenschaften, 86(11), 552-555.
Hoffmann, J., Donoughe, S., Li, K., Salcedo, M. K., & Rycroft, C. H. (2018). A simple developmental model recapitulates complex insect wing venation patterns. Proceedings of the National Academy of Sciences, 115(40), 9905-9910.
Jongerius, S. R., & Lentink, D. (2010). Structural analysis of a dragonfly wing. Experimental Mechanics, 50(9), 1323-1334.
Li, X. J., Zhang, Z. H., Liang, Y. H., Ren, L. Q., Jie, M., & Yang, Z. G. (2014). Antifatigue properties of dragonfly Pantala flavescens wings. Microscopy research and technique, 77(5), 356-362.
Norberg, R. Å. (1972). The pterostigma of insect wings an inertial regulator of wing pitch. Journal of comparative physiology, 81(1), 9-22.
Rajabi, H., Ghoroubi, N., Stamm, K., Appel, E., & Gorb, S. N. (2017). Dragonfly wing nodus: a one-way hinge contributing to the asymmetric wing deformation. Acta biomaterialia, 60, 330-338.
Rajabi, H., Shafiei, A., Darvizeh, A., & Gorb, S. N. (2016). Resilin microjoints: a smart design strategy to avoid failure in dragonfly wings. Scientific reports, 6, 39039.