We dragonflies (odonata) are among the most striking forms of insects. In the bright sunlight we fly, hunt, court, we pair and lay eggs. We live out our lives before your very eyes. It’s probably our spectacular flying that amazes you the most. In fact, I can name nine distinct types of flight which we have completely mastered: neutral flight, cargo flight, patrol flight, menacing flight, mating flight, commuter flight, wave flight, hover flight – as well as many varieties of backward flight.
Among the 800,000 kinds of insects, we are the only true acrobatic fliers. For hours at a time during warm summer days, we drift back and forth over a pond, hardly moving our wings at all. If we see an edible insect, we seize it instantly with a lightning fast movement.
If an annoying rival arrives on the scene, we spiral into the air and circle him until he flies away. Even in swamps, we are able to fly through the dense vegetation with elegance and style, without ever bumping our sensitive wings against anything. As you already know, we rule the air near water. We move around like silent helicopters. Even though we beat our wings at a frequency of 30 cycles per second, we make no sound that you can hear. Our wings don’t just serve for flying. They also play an important role in the competition for mates. We use them for balancing on precarious perches. We even use them to absorb warmth from the sun. And the tongues of aggressive frogs encounter them as sharp defensive weapons. But still, flying is and remains their chief purpose.
Of our 4,500 different varieties, 80 are present in Central Europe. We are divided into two groups: Large Dragonflies (Anisoptera) and Small Dragonflies (Zygoptera). Of the many different names, I’ll just mention a few, so that you’ll get an idea of how varied our family is:
Small Dragonflies:
White-legged damsel-fly, Coenagrionidae (for example the Scarce Ischnura), the green lestes, the Calopterygidae.
Large Dragonflies:
Hawkers, (for example, the southern hawker, Emperor dragonfly), the dragonfly, cordulegastearidae, emeralds (for example, the brilliant emerald), and libellulidae (for example black-likened ortetrum, black-tailed hawkers, vagrant sympetrum, vagrant darter).
Most of the medium-sized dragonflies belong to the first classification of Small Dragonflies. The larger ones are in the second group. But size is not the most important element in our classification, because some of the smallest of the large dragonflies like the vagrant sympetrum – are three centimetres long, and the largest of the small dragonflies – the calopterygidae – is five centimetres long. It is much easier to classify us by our wings. When they rest, the small dragonflies fold their similar sized front and back wings together. The large dragonflies spread their different sized wings out from their bodies. In flight, too, there are essential differences: the small dragonflies move their front and back wings at different rates, while the large dragonflies’ nervous system synchronises their wing movements. For now, I’m only going to talk about the large dragonflies. Your (German) poet and zoologist Hermann Löns (1866 – 1914) was so impressed by the Emperor dragonfly that he wrote:
“None of the other chalcolestes viridis comes close; it is more beautiful and swifter than the large anisoptera. Its wings are formed of gold filigree, emerald green jewellry adorns its head, and its body wears finery of black-traced azure blue silk.”
Aerodynamic Body: Like all insects, our body consists of three segments: head, thorax, and abdomen (Fig. 1). But our construction includes numerous special features that are especially adapted for our lifestyle, and particularly for our ways of flying. Our matchstick long, thin abdomen, which looks like a balancing stick, is remarkable. It actually stabilises our flight, and conceals our digestive and reproductive systems. Our segmented construction and the connecting skin provide high elasticity and good manoeuvrability. Every individual segment consists of hard breast plates and strong backing, just like an ancient knight’s armour. Our Creator used Chitin for our external skeleton. This special material is extremely light, and is hardened by calcium deposits. Thanks to this two-component system, we have a skeleton that combines extreme strength, with minimal weight. Thus a Horse-shoe Blue dragonfly weighs only one-fortieth of a gram. That means you would need 80 of these small dragonflies to match the weigh of a single one-cent piece.
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| Figure 1: The basic body structure of a dragonfly. |
Legs for Catching
Instead of Walking We rarely use our thin and remarkably thorny legs for walking. But they are very important when we are flying. Normally, we tuck them in close to our bodies when we are flying, to minimise air resistance. But if we see prey, we spread our six legs out in front of to us form an opened “catcher”, so that we can “fish” our snack out of the air. Our inflight menu consists of ephemera, mosquitoes and moths. Since we can only spot our prey at close range, we only have a fraction of a second to complete the flight manoeuvre and actually catch the target. Our eyesight, our nervous system’s ability to react, and our flight technique are stretched to the limit by the high targeting accuracy required to catch our prey.
Our Flight Equipment
– Forerunner of Your Helicopter
We have completely different principles for flying from any other insects. The Creator developed a special kind of equipment for us. And I’d like to tell you about it now. Most insects fly by a so-called “tea-pot” principle. Just imagine a pot with a lid that is a little bit too small and two spoons which have been placed under the edges of the lid. If you push the lid down, the spoons rise up. If you lift the lid, the spoons drop. In most insects, this pressure is supplied by muscles that are found in the thorax area, which are connected to the “lid” and to the “bottom of the pot”. With every muscle contraction, the body tightens up, and this raises the wings. The opposite motion occurs when the muscles are relaxed. In contrast, our flight motor operate on a fundamentally different principle.
Our strong flying muscles are connected directly to the wing joints by tendons. The Creator made these tendons out of a material called resilin, which has extraordinary mechanical properties. Unlike any other material, it is completely elastic, and can therefore store a huge amount of energy which can be released at the necessary moment. Picture a flattened plastic bottle which springs back to its original shape immediately after being squashed. Together, the wings and the resilin form a similar system to that of the bottle, and have a particular oscillating frequency.
Our Creator designed us with so many of the intricacies of flight built in, that we are well able to take care of ourselves once airborne. We were simply made to fly. Your aeronautical engineers have a way of describing flight characteristics in terms of the socalled Reynolds number. It characterises the relationship between the viscosity of the surrounding air, and the speed and size of a flying object. For large birds, this air coefficient is of little or no importance, but it’s a different story for insects. Actually, for small insects, the viscosity of the air is such an important factor that they really tend to swim through what is for them “thick” air. Insects with a small Reynolds factor must beat their wings much faster than larger insects just to make headway. It turns out that our Creator gave us a very favourable Reynolds coefficient. We can easily reach speeds of 40 km/h without constantly having to beat our wings. Even when flying slowly, enough lifting force is generated by the air streaming over our wings to keep us aloft.
Forehead Anemometer:
In addition to an effective flight propellant, speed control is necessary for optimal flight. The Creator installed two antennae on the front of our heads, at the optimal position for measuring air flow. In flight, these feelers are bent back by the air in the slipstream. Sensory cells in the base of the antennae transmit the measured values to the brain, where the data is used to calculate speed in relation to the environment. For flight precision as well as style, these measuring antennae are one apparatus I simply couldn’t do without.
Wing Membranes Thinner than Paper:
The combined weight of our four wings is a mere five thousandths of a gram. This wafer-thin, transparent flight apparatus is a masterpiece of lightweight construction technology. If you were to imagine our wing membranes forming the material of a large surface, then a square metre would weigh only three grams. The cellophane you use for wrapping, made of polyester or polyamide has to weigh three to four times as much to have the same strength. Our wings are reinforced by veins – your aeronautical engineers would call them “spars”. The diameter of these tubes is only 1/10th of a millimetre, and the thickness of the walls of the tubes is only 1/100th of a millimetre. These hollow tubes serve not only for bracing the wing, but are also the transport lines for the blood fluid (haemolymphes), and the data cables of the nervous system, as well as the system for oxygen supply and carbon dioxide removal.
Calculated Security:
If you have come to the conclusion that the Creator skimped on safety by saving on materials, then please permit me to put the record straight.
All living creatures are provided with safety reserves just as they are in your technology, so that premature breaks and failures do not occur. For example, you could withstand the weight of 17 men on your thigh bone. You need this reserve for running or jumping, in order to withstand greater stress. In the mouse, the thigh bone is able to withstand a load of up to 750 times the usual. After all they have to be able to jump from a kitchen cabinet, without breaking a leg. The same goes for wings. A chaffinch, for example, has a total wing surface of about 150 square centimetres, for a body weight of 25 grams. That means that 10 square centimetres of wing surface support 1.7 grams of body weight. The 15 square centimetres that we dragonflies have, support a mere 0.5 grams i.e., 0.33 grams is supported by 10 square centimetres. This corresponds to a security margin that is five times greater than that of the chaffinch. You wouldn’t have expected that now, would you?
Wing Pattern as Personal Identification:
Our wings are glass-like membranes, reinforced by many branches of a network of circulation tubes. The longest arteries give cross-sectional stability, while the many small branching arteries, and the clearly visible “wing marks” (pterostigma) provide longitudinal stability. A glance at the wing pattern of the blue-green Southern Hawker and that of the Mecistogaster lucretia, reveals that the Creator used distinctly different construction principles to achieve the same purpose: irregular polygons and regular rectangles provide the necessary wing stiffness in each case. Dragonflies with a higher wing beat rate, like the blue-green Southern Hawker (30 beats per second) need to have narrow reinforcements. Other kinds with a lower wing beat rate can get by with simple, but unbelievably precise, right-angle lattice pattern. An example of this is the Mecistogaster Lucretia with its long, thin wings, beating 15 times per second. The membrane cell construction technology makes the wings ultra-light, but still very stable. Plus, if you have an eye for design, you can tell our different varieties apart just by examining the varying arrangement of the lengthwise and transverse wing arteries. The significance of the reinforced edge cells on our wings was only recently discovered by the Swedish scientist Ake Norberg. The species dependent variation in cell thickness towards the tips of the wings also has an important aerodynamic function. In high speed diving and gliding flight, they prevent so-called wing flutter.
Turning Flight:
For turning flight, we utilise a special technique which again differentiates us from other insects. Split seconds before a turn, we twist our body on its long axis. Viewed from the front, the thorax and abdomen are no longer lined up horizontally, but are displaced. A different angle of attack is then created for our inside wings which enables us to make elegant curves. Other insects – beetles in particular – utilise a different principle: the wing on the inside of the turn beats in a smaller angle. In this way, the thrust on that side is reduced, and the desired turning motion takes place even with the same wing beat rate.
No Honeymoon Flight Without Previous Code Check
You have already heard some of our most remarkable characteristics. But if I were to tell you about our mating habits, you would certainly think that these are not just unusual, but really quite original. Since we are designed for flight from head to toe, we think it is totally natural to mate in mid-air. That’s got your attention! And, I’m sure you’re now thinking about the many constructional details that would be necessary for something like that. You probably think that the flight manoeuvres alone would be impossible. Actually, the Creator didn’t run out of ideas, and even here, He came up with something special for us. Just listen: Before the wedding, the male’s courting flight takes place. This mating flight is marked by rapid wing movements around the cross-axis, whereby the wings beat alternately. To the approaching female, this appears as a thin blue side band. Needless to say, this is not unattractive to her. In the forward flight phase, the front wings beat with a reduced angle of frontal attack. They provide the lift to remain aloft. The back wings beat at a high angle of attack to the rear, and thus achieve maximum propulsion. For split seconds, conditions are reversed. Now the rear wings take over propulsion. In backwards flight – our flight speciality – everything works in reverse. The steeply angled front wings produce the necessary force to make backwards flight possible. The back wings are adjusted almost horizontally, and provide the necessary lift.
The male now flies to the female from above, and seizes her on the head with the so-called abdominal hook (in the case of small dragonflies, the female is seized by both the head and the first thorax segment). This big semicircular “tong like” apparatus sits at the very end of the long abdomen, and serves to anchor the two insects firmly together during mating. In the middle, between the hooks, are a pair of short appendages which vary from type to type. These fit into a matching system in the female, in a “key-lock” arrangement. This ingenious code system ensures that only the same types of dragonflies mate with each other. After this secure grip is established by the identifying code system, the partners form the “mating chain” in tandem flight, male in front female to the rear.
This peculiar wedding is necessary because of another unusual part of dragonfly construction. All dragonflies carry their sex organs at the end of the abdomen. But how can the male sperm get to the female? The solution of this riddle lies in an ingenious idea: the male sex organ has two functions. The sperm is produced at the end of the body, and then is transported to the “appropriate place” into a sperm pocket. Depending on the type of dragonfly this happens either before or after the two unite: the male bends the rear of his abdomen into the sperm capsule of the secondary copulation organ, and thus fills it.
Now the female bends the rear of her abdomen down and forward so far that her sex opening at the end of her abdomen reaches to the sperm-filled holder on the second and third abdomen segment of the male. In this way, the mating chain is altered to form the “mating heart” or the “mating wheel”. After the successful transfer of sperm, the mating wheel is released. Now in tandem flight, the pair fly to the place where the eggs are laid. In this, the leading male directs the way to an appropriate egg-laying location. In the case of meadow dragonflies, the landing takes place on alder or willow branches that hang over the water surface of a pond. Now the most difficult part begins for the female: 200 eggs must be deposited under a hard bark surface. Do you have any ideas how this can be done? A tiny saw on the laying borer of the female serves as an effective tool. The sawing action, which deposits tiny particles of dust in the water, takes just a few seconds. Then the long eggs are laid in the moist cells of the bark. During this long procedure, which can last up to four hours, the male appears to be idle. He is in fact protecting the neck region of the female with his legs, keeping her free from other males eager to mate, who lost out in the mating competition.
You may well ask, “Why bother with such an unusual mating method?” Well, for us, everything has to be arranged for absolute flight-worthiness. So we take to the heights of the air even during mating. In this sense, you could consider our independently movable front and rear wings as special equipment. In hovering flight, we are even able to move our wings against each other. Because of our flight technology, we need our lengthy abdomen as a balancing beam. Especially during the complicated manoeuvres of mating, we need to be able to stay absolutely motionless in the air. The pin-point coupling, even in turbulent air, requires unparalleled flight precision.
Did you know that the pioneer of your helicopter technology, Igor Sikorsky (born in 1889 in Kiev, died in 1972 in the USA), got the idea for the development of the helicopter from his dragonfly observations? The four adjustable rotor blades enable both forward and backward flight, just as our four wings do. In spite of the well-known technical capacity of your flying machines, the capabilities of your helicopters and of ourselves, are worlds apart. Our flight is a hundred times more nimble, and absolutely silent. A gentle rustle indicates our flight when our wings touch. But it all takes place with an unmatched degree of efficiency.
Our Remarkable Eyes
Whoever wants to manoeuvre fast and gracefully has to have user-friendly navigation instruments. And so, we have our ball-shaped, knitting-needle-head-sized eyes. Among all the insects, we are the real “eye animals”, because our seeing apparatus composes the majority of our head surface area. The high degree of curvature creates an extremely wide field of vision.
Our eyes are composed of up to 30,000 six-sided individual facets. Each of these facets forms a distinct eye with its own tiny lens. This gives each eye an individual angle of vision. All of them together cover a very broad field of vision, without any individual eye, or the head, having to move. Our eyes are much more capable than yours in many ways. We are able to perceive 200 blinks of light per second, while you can only perceive one tenth of that. If there were television for dragonflies, a film intended for us would have to be transmitted at ten times the speed of your TV stations.
Let me talk about some of the physical principles involved here. In contrast to your eyes, the image arising from up to 30,000 individual eyes is actually quite imperfect and unclear. While each of our eyes contains only eight vision cells, you have 78 million. So you have an image that is scanned much more finely. This implies that our visual acuity is only a fraction of yours. Nevertheless, we have a wonderful imaging system, full of the Creator’s technical refinement, that substantially increases the quantity of the given visual information. Rapid sequential bursts of light, up to 200 per second, are individually registered as separate events. Our movements are almost exclusively flight movements, whereby we perceive the environment as being in constant motion. In flight – and again, that is our primary activity – the optical centre receives substantially more information than when we are at rest. Our “flight” visual acuity is thus substantially greater than you would expect from the anatomical construction alone. Our vision is approximately the same as that of your TV cameras: the light beam with which the image is sampled is comparable to the function of each individual eye. The beam alone is unsuitable for picking up the smallest detail of the form of an image. But if you move the beam, and display the variations in brightness that arise by sampling the image in sequential impulses, one can obtain a detailed image of the observed object. So your TV and my compound eye generate an image in much the same way: both systems use a combination of highly developed fast processing power, together with low resolution optical imaging equipment.
Our Coloured Dress
Even if you have gotten to know our insect species fairly well, I dare not neglect one characteristic. It is our impressive colouring! After the butterflies, we take the second place in the competition for beauty and colour. With us, you can find every colour imaginable: from sharp colour tones, to metallics, to dark and rich hues. How do all these nuances and colour compositions come about? I won’t explain these colours scientifically, otherwise I would have to delve into the sophisticated knowledge of chemistry, as well as going back to physics. But there are three independent principles which you should know:
1. Pigmentation:
Why are Chinese yellow, Indians red, and Africans black? Well, there are certain colour substances, pigments, in their skin which are character istic for these races. This is exactly the method the Creator used to colour certain types of emeralds, for example the vagrant darter, as well as some of the smaller dragonflies. In contrast to your races, our chemical bonds produce a substantially stronger colour effect, as for example, melanin for yellow, red, brown and black, ommine for violet brown and ommatine for red brown tones. In the same way, white, yellow, or reddish pterines are used. You can well imagine that the appropriate mixtures of these colouring agents permits a rich display of colour.
2. Structural Colours:
With this method, the colours are not produced by organic molecules, but by means of a physical trick. The colour impression comes by means of light diffraction of the rays of sunlight falling on thin, platelet-like layers of chitin armour. All metallic shimmering dragonflies are actually colourless, but still, they glisten in richly coloured splendour. Such structural colours are seen for example in the blue-metallic calopterygidai, the green to copperish green lestes, and the shining green Brilliant Emerald. The Coenagrionidae and Aeshnidae dragonflies, with their enamel-like green and blue, also have additional dark bodies in their chitin armour causing light dispersion, which enhances the multiplicity of colours even more.
3. Wax Colours:
This method is reminiscent of the coating seen on ripe plums. The bluish ripening of the abdomen on the common green lestes comes from a wax coating that is produced by skin pores. The colour arises by diffuse reflection of the sunlight.
What is the purpose of all these colours? The various kinds of colour patterns make it easier for us to recognise various species, and also makes it easier for us to find a mate. Colouration can also serve as a good camouflage. As we are animals with varying body temperatures, colouration helps us to warm up in the mornings. In the same way, our colours give us appropriate protection from ultraviolet radiation, and regulate the force of sun radiation we receive. But still, all these effects could have been achieved with a much lower number of colours. The astonishing variety must have another reason: it is the Creator’s richness of invention, and His love for beauty. Speaking of the lilies, the Lord Jesus said,
“Look at the lilies of the field, how they flourish… I say to you that even Solomon in all his glory was not clothed as one of these” (Matthew 6:28-30).
We come from the same Creator’s workshop. So you shouldn’t be surprised at our beauty and glorious colour.