Over millions of years, thousands of species have evolved from one single prokaryotic cell. Some have developed shells, some have developed walking legs, some have developed wings, and all of these developed for one common purpose: survival. All these adaptations have a specific purpose and have been refined over the years, due to environmental changes, evolution of new predators, and more, and continue to adjust in an ever changing world. One clear example of this is a dragonfly’s flight pattern and wings which allow them to thrive in their different environments all over the world. Their two pairs of wings are independently controlled, which makes them unique to others in the animal kingdom, including other insects and birds, and makes them an interest to humans who are looking to improve aerodynamics of man-made flight (Sun et al., 2016).
In the class Insecta, under subclass Pterygota, there is an order Odonata which encompasses two suborders of animals, commonly known as damselflies and dragonflies. Those suborders are scientifically known as Zygoptera and Anisoptera, respectively. There are many characteristics that set this order apart from other insects in their class. They have extremely small antennae, very large eyes that take up most of their relatively big head, a long, skinny abdomen, a nymph stage with posterior tracheal gills, and an extendible jaw under the head (Sabet-Peyman, 2000). However, even though they share all these characteristics, they do have noticable differences that separate their suborders. For example, damselflies fly slower than dragonflies due to their forewings and hindwings have a similar shape. In dragonflies, their rear wings have a wider base and are observabley bigger than their forewings (Sabet-Peyman, 2000). In, addition, damselflies have the ability to fold their wings together when resting, while dragonflies can not. Dragonflies wings form in the nymph stage and when transitioning into adulthood, the wings uncurl while filling with hemolymph, then most of the blood is transferred back to the body causing the wings to stiffen (Mead, 2010). The order Odonata are known as ancient insects and the oldest fossil is of Protodonata, which is now extinct. The fossils date back to the lower Permian, over 250 million years ago, when their wingspan was around 30 inches (Sabet-Peyman, 2000). The suborder Anisoptera eat whatever they can find, especially small insects such as ants, termites, and gnats. Their many predators include birds, lizards, frogs, fish, spiders, and more. Despite their abundance of predators, damselflies and dragonflies have been able to survive for centuries, and are living evidence of evolution.
As for where dragonfly wings originally evolved from, there are two hypotheses, because there is not a clear lineage of ancestors. One hypothesis states that insect wings evolved from a portion of an arthropod’s leg, although they are not clear which leg it derived from (Jockusch & Nagy, 1997). The thought is that wings are a homologous structure of a proximal leg seen in arthropods, and moved to the dorsal side of the thorax by moving around the circumference of the body (Jockusch & Nagy, 1997). The other states that wings arose brand new out of the thorax, with no common ancestor (Jockusch & Nagy, 1997). Many scientists have conducted research to solve this debate of how wings came to be, however until there is clear lineage from leg to wing, then it is all speculation. It is also unclear if multiple winged insects arose Regardless of how they evolved, it is clear that they of significant importance to the insects survival and life. Wings can serve a number of purposes in the insect world, including flight to catch prey and escape predators, attract mates, act as protection (as seen in beetles, especially), camouflage and much more. They are helpful in catching prey and disappearing from predators because it is an efficient, stealthy and fast approach to locomotion. It attracts mates due to their colors, and the noises that some insects make when flapping their wings, such as crickets. Beetles are a good example of how wings can provide a protective cover to their soft bodies. Their wings have formed over time to become harder to save them from predators and things falling of them. Lastly, some use their wings as camouflage for the common theme of survival. There are many more reasons, but that is just to name a few. Without wings, dragonflies would not be able to escape seasonal droughts and likely die from being unable to migrate. Fast locomotion is a key characteristic of this insect.
Dragonflies have four wings, each with different muscles to maneuver them. They can use their wings together to flutter in sync, or use them separately. This allows them to hover like a helicopter for up to a minute, soar up to 90 kilometers per hour, or 100 body lengths per second forwards. They can also perform tricks that are unique to their suborder, such as flying backwards up to three body lengths per second, upside down, and loop de loops (Bickel & Walker, 2013). Many scientists and photographers found their flight interesting when they noticed that the dragonfly would hover for a bit and then immediately fly quickly to another location to hover again. Because order Odonata is one of the most ancient insect orders, dragonflies have not changed their basic body plan in around 350 million years, meaning that the characteristics they have work for them, and that they have had time to learn how to optimize things such as their ability to be more aerodynamic, save more energy, etc. (Wang, 2008). They can flap their wings at a rate of 30 beats per minute, or 40 Hertz, creating whirlwinds in the air that push them upward (Wang, 2008). When taking off the dragonfly beats their wings simultaneously, however, when hovering in one location their forewings beat out of sync with their hind wings (Wang, 2008). This means that their ability to be more aerodynamic is enhanced when they beat together and is expelled when beating against each other. It also means that the drag and net force affecting both pairs of wings when beating out of phase is essentially at equilibrium, making them stay in one spot (Wang, 2008). When hovering, dragonflies are saving energy, but while moving and taking off they are using a great amount of power and energy.
Dragonfly wings are composed of many veins and two, thin, outer membranes that, collectively, make up merely two percent of their bodies weight (Sun et al., 2014). Despite this, they are able to retain their shape, stability and carry heavy loads relative to their mass, even during flight, fluttering and hovering (Sun et al., 2014). Although there are many variations between genuses, all of suborder Anisoptera have common purposes for what their wings are composed of and how they are formed. The two outermost membranes, which are made mostly of chitin, add strength to the wings, as chitin is a key compound in many other animals hard exoskeleton (Bickel & Walker, 2013). Chitin also gives them, and other insects in the animal kingdom their glossy, shiny, and smooth appearance, especially when the wings lack pigment (Bickel & Walker, 2013). If the wings do have a lot of color, it is most likely a strategy to attract a mate, but their wings will usually appear to be less glossy. The wing’s structure is also full of veins that allow them to flex and curve while flying through the air. The veins in the wings are thick and stem from their bodies to protect them from deformations, and keep them stiff enough for flight. The blood enters these veins through the thorax of the insect, flows to the wing apex and through the large anterior veins and then returns to the body (Wang & Zhong, 2014). The veins also determine the wings shape, which is dependant on what is most beneficial for its environment (Sun et al., 2014).
There are many factors that affect an animal’s wing shape. For example, they can be altered depending on the insect’s migration distance, mating strategies, where they live, size of their bodies, and/ or hunting techniques (Johansson, 2009). Although many dragonflies stay close to the water in which they emerged, some can migrate several hundred kilometers to avoid droughts. It is thought that, similar to bird wings, dragonflies who travel farther have a longer, more slender wing shape, because it allows them to move faster and save more energy (Johansson, 2009). However, only “25 to 50 of the world’s approximately 5200 dragonfly species are thought to be migratory,” which makes the insect more difficult to study and find trends for (Johansson, 2009). In regards to how mating can affect a species, male dragonflies, who have, on average, longer and narrower wings with a wingspan from seventeen millimeters to twenty centimeters, have been observed to guard the female when she lays her eggs, which affects both the male and female’s wing shape. One strategy for the male is called tandem guarding, where the male will hold on to the female and fly together as one. The wings for those who take on this type of mate guarding tend to be broader and more pointed toward the the outer front of the wing (Johansson, 2009). The other strategy is called non contact guarding where the male will fly close by, but separate from the female. These dragonflies wing tip is usually pointed in the opposite direction, the outer back, and are skinnier in the outer half of the wing in comparison to those who tandem guard (Johansson, 2009). Depending on which mating strategy the genus adopts, in addition to whether that specific dragonfly migrates a long distance or not, and whether it is female or male, the wing shape must evolve differently.
All dragonfly wings have an intricate pattern that has been studied over and over again. From these studies a few commonalities have risen. Each wing has what is known as a stigma, which is an unpatterned section located on the leading edge out toward the wing tips, which is thought to be used to attract mates (Mead, 2010). It also is used as a tool to aide in flying by acting as a weight to make the wing strokes more powerful. Another section of the wing that helps its flight have more function is the nodus. The nodus is located at the midway point of the wing where there is usually an indent. It separates the two halves of the wing, the proximal and distal. Due to it being an intersection of large veins, it provides more flexibility and strength to the whole wing, especially in flight (Mead, 2010). When the wings are coming upward, the nodus has the ability to flex downward to glide in the air, but stays straight when the wing is coming downward, saving energy (Mead, 2010). Some species have what is referred to as an open- nodus, while others have a closed-nodus. Those with an open-nodus structure have the highest flexibility, which works well when the animal is flapping, but also is more prone to over-bending, which is detrimental to gliding flight (Zhang et al., 2018). Those with a closed-nodus also have a flex-limiter, making this the least flexible at high wind speeds which almost eliminates the over-bending problem, making them great gliders, but not as good of flappers (Zhang et al., 2018). Overall, the nodus prevents any fractures on vein structure during flight, allows the wing to deform to become more aerodynamic, provides flexibility, which is limited by the flex-limiter. In addition, the closed-nodus structure “wing is [most] suitable for gliding flight due to its low amplification ratio.” (Zhang et al., 2018).
However, they have more flying stages than just the ones mentioned previously. The first is gliding, where dragonflies do not move either pair of wings and it allows them to move 40 chord lengths with a single beat of their wings (Sun et al., 2017). This allows them to move far distances and stay in the air with little effort or energy expelled. It is also the simplest form of flying that is seen in these animals. Hovering, in contrast, is used when a dragonfly is hunting. They are able to stay stationary while looking at their prey and they can make slight alterations of where they are facing to better prepare themselves to catch what they are hunting (Sun et al., 2017). Their wings, as mentioned before, beat out of sync with each other, but at the same speed in this type of flying causing them to have a fet force of zero. The next type of flying is accelerated. This takes an immense of power and therefore can only be done in short bursts, but generates a great amount of speed. The insect beats their wings together at the same speed and in phase with each other, making the animal take off, or lift to catch prey (Sun et al., 2017). Cruising flight is what is seen most commonly in day to day life, it is the middle ground between hovering and acceleration. Also known as forward flight, dragonflies beat their wings separate from each other but not exactly opposite of each other as seen in hovering (Sun et al., 2017). Lastly, free flight is observed when the insect turns, or does what we see as tricks. It can turn 180 degrees in a mere 3 wing beats, however it is still too complex for scientists to make any conclusion of how or why they do these things.
It is so common now that our world has become so advanced with technology to study and observe animals in their natural habitat. As humans, we can observe an animal’s adaptive characteristic and use it as inspiration to find a solution for a medical, construction or technological problem. Due to this, dragonflies flight techniques as well as their vein patterns and wing structure have increasingly caught the attention of humans all around the world. One study used their findings of dragonflies wing venation to create a lightweight, efficient, and stable greenhouse roof (Sun et al., 2014). Other studies, more obviously, used their findings of dragonflies aerodynamics and flight to figure out ways to improve helicopters and airplanes. However, as useful as this information may be to humans, some species of dragonflies are endangered and very close to extinction, due to pollution, habitat loss, and changes in groundwater. Just as humans are able to benefit from dragonflies innate flying capabilities, we need to help them by reducing our use of chemicals, especially on lawns, recycle our car oil, and protect their habitats so that they can live another million years (Anonymous, 2006). They have survived 350 million years and as living fossils deserve to live on, coexisting with humans. Overall, dragonflies wings are useful not only in catching prey and escaping predators, they have taught humans a lot about aerodynamics, speed, and flight capabilities while expending little energy. The way that their wings have stayed relatively the same over millions of years, and yet their flight is so advanced, teaches us that nature has the best solutions to the world’s problem.