Spotted darter ( Sympetrum flaveolum )
|Fabricius , 1793|
The dragonflies (Odonata) form an order within the class of the insects (Insecta). Of the 6,323 species known in 2019 , around 85 occur in Central Europe. The wingspan of the animals is usually between 20 and 110 mm, the species Megaloprepus coerulatus (Zygoptera, Pseudostigmatidae; thus a "dragonfly") can even reach a maximum wingspan of 190 mm. The science of dragonflies is odonatology .
The dragonflies are characterized by an extraordinary flying device. The ability to move their two pairs of wings independently of each other enables them to make abrupt changes of direction, to stay in the air or, in some species, even to fly backwards. Maximum speeds of 50 km / h are reached during flight. The frequency of the wing beat is relatively slow with about 30 beats per second.
The large fore and hind wings are (especially in the small dragonflies) almost the same size. The wingspan of the animals ranges from 18 millimeters in Agriocnemis pygmaea to 19 centimeters in Megaloprepus caerulatus , Pseudostigmatidae. Since they lack the wing joint typical of the new winged wing, they cannot put the wings backwards over the abdomen. In contrast to almost all other flying insects, the dragonflies' flight muscles attach directly to the wings.
The wings are stabilized by a complex wing veining . The flight area is not flat across the longitudinal veins, but spanned in a zigzag shape. In the center of the wing, these veins meet at a junction (nodus) so that they cannot kink even if they are subjected to longitudinal stress. Overall, the veining of the wings differs greatly in the various dragonfly species, so that it can be used as a characteristic and for the systematic classification of the animals.
At the front area of the wing tip, most species have an enlarged and dark-colored wing field, which is called a pterostigma and which can be used in flight as a trim tank by filling it with hemolymph.
The head of the dragonfly is clearly separated from the breast segments and therefore very mobile. The large compound eyes , which in some species can consist of up to 30,000 individual eyes ( ommatidia ), are striking . Between the complex eyes, on the top of the head, there are also three small point eyes (forehead ocelles), which probably serve as an organ of equilibrium (horizon detector) and to control rapid flight movements. Experiments on the hawk dragonfly Hemicordulia tau provide information on this , the flight of which becomes unstable when the ocelles are covered. With this system, they probably have the best sense of sight among insects.
The antennae of the dragonflies are bristle-like short and consist of eight segments. Their function is mainly to determine the airspeed, which they determine with the help of the sensory hairs on them.
The mouthparts and especially the mandibles are strongly developed and toothed (hence the scientific name "Odonata"). At the front these are closed by the upper lip ( labrum ). The maxillae each have a button and the lower lip ( labium ) has two lobes.
As with all insects, the chest ( thorax ) of dragonflies is made up of three parts. The two rear breast segments are very strong and oriented at an angle to the first segment. In this way, a forward-facing “basket” emerges from the legs. These also have strong claws and are usually thorny on the lower leg ( tibia ) in order to better hold the prey.
The elongated abdomen consists of ten segments. Due to the length it stabilizes the flight. The mobility of the abdomen is primarily necessary for the mating of the animals. At the end of the abdomen, the males have gripping pliers made of modified abdominal appendages ( cerci ), with which they can hold the female while mating. The dragonflies have an upper pair (Cerci) and a lower pair (Paraprocte) abdominal forceps. The lower pair of pincers is missing in the dragonflies and instead there is an unpaired movable appendage (epiproct). The males also have a secondary copulatory apparatus on the abdomen, the females an egg-laying apparatus ( ovipositor ).
Dragonflies are mainly found near bodies of water , as their larvae depend on water for their habitat. A particularly large number of dragonflies, such as the blue-green damsel Aeshna cyanea, also fly over large areas away from the water to catch prey. Dragonflies move away from the water for a few weeks, especially during the maturation phase. The females are usually not found near the water, as otherwise they would be forced to mate immediately by a male. Some dragonfly species are also not uncommon to be found in suburban areas and green residential areas.
Running and standing waters
Only relatively few dragonflies are pronounced flowing water species , especially in the fast-flowing upper reaches and in the source area you will only find well-adapted animals. In these areas live mainly the spring maidens of the genus Cordulegaster , whose larvae are dependent on the oxygen-rich water of these waters. However, these can be found in the quieter areas behind stones or water plants. The two-striped spring damsel Cordulegaster boltonii can also be found in slowly flowing waters.
Typical inhabitants of the rivers and slow streams are the dragonflies (genus Calopteryx ) and the river maids (Gomphidae). At narrow ditches and meadow brooks, for example, the Helmet-Azure Damselfly Coenagrion mercuriale and the Vogel-Azurjungfer Coenagrion ornatum can be found .
Far more species prefer stagnant water as a habitat. They can be found in ponds , lakes and ponds , where their larvae live mainly in the shallower bank zones and between aquatic plants. Some species, such as the great pitch dragonfly Ischnura elegans , the horseshoe azure damsel Coenagrion puella or the blue-green mosaic damsel Aeshna cyanea are hardly specialized as so-called ubiquists , and many dragonfly larvae can also tolerate relatively high levels of pollution . More specialized species such as some darter (genus Sympetrum ) need certain types of small bodies of water, such as B. periodically drying shallow waters, or even swamps.
“Almost every one of these pasture grounds contains a water surface, surrounded by irises, from which thousands of small dragonflies hang like brightly colored sticks, while those of the larger species purr up to the middle of the pond, where they enameled into the leaves of the yellow nymphaea like golden decorative needles Shells fall down and there lurk for the aquatic insects on which they feed. "
A particularly endangered habitat are the moors , which also serve as a habitat for many species of dragonflies. These species are adapted to the conditions that exist here, such as the extremely low pH value of the waters and the sometimes very low oxygen resources and can therefore only survive with difficulty in other habitats. Various azure maidens live here too, such as the spear-azure maiden , Coenagrion hastulatum , falcon dragonflies such as the arctic emerald dragonfly Somatochlora arctica, as well as maidenheads like the peat maidenhead Aeshna juncea . Most of the moss damsel (genus Leucorrhinia ) are particularly typical bog species .
Way of life
The prey of the dragonflies consists essentially of other insects, whereby the spectrum is very large. Dragonflies attack almost indiscriminately any animal they can overwhelm. The males in particular also attack other dragonflies during the mating season, sometimes even members of their own species, thus showing cannibalism . The hunting flights are not limited to the water, they also take place in meadows, forest clearings or other open areas. Some species, especially dragonfly species from tropical regions, but also the native green mosaic maiden ( Aeshna viridis ), are real twilight hunters. They are completely dependent on their eyes to find the prey.
Like many other insects, dragonflies use the heat of the sun to heat their bodies, especially their muscles. For this purpose, some species sit in sun-exposed places and spread their wings to store the heat under the wings. This behavior is particularly common in species from the cooler mountain regions.
Despite their speed, dragonflies have a large number of predators. They are particularly vulnerable when they shed their skin for the last time and work their way out of exuvia . Frogs , bats and birds in particular eat dragonflies, but wasps , spiders and ants can also attack and consume newly hatched dragonflies. Also, carnivorous plants such as the sun rope ( Drosera ) are for dragonfly to danger. The parasites of dragonflies mainly include the larvae of water mites , especially those of the genera Arrenurus and Limnochares in Central Europe . The larvae of dragonflies fall prey to other dragonfly larvae, but also to other predators in the water.
Reproduction and development
Mating and laying eggs
The two adult dragonflies are found in flight, whereby after a foreplay the male grabs the female with the forceps from the two abdominal appendages at the back of the head ( large dragonflies ) and on the prothorax ( small dragonflies ). The resulting pairing chain is also known as a tandem position. After the male has filled his secondary copulatory apparatus, the female bends forward in flight and touches the male's seminal receptacle on the second or third abdominal segment with its genital opening on the eighth or ninth abdominal segment. This creates the pairing wheel typical of dragonflies .
There are species in which the male transfers the sperm in flight. The females are typically mated by several males in the course of their life; there are ways in which the male clears out the sperm of another male before transferring his sperm.
After mating, the female usually lays the eggs in a body of water. There are species that pierce the eggs into aquatic plants (endophytic), and those that drop the eggs into the water in flight or strip off the substrate underwater (exophytic). Other species pierce the eggs into the bark of trees on the bank (for example, willow damsel ) or, like some darter, shed the eggs over dry depressions that may later be flooded. Eggs can be laid in tandem or by the female alone. What is astonishing is the ability of the females of some species (for example dragonflies , common cup maiden ) to dive completely under water for up to 90 minutes to lay eggs. They take an air bubble with them between the body and both wings to breathe. Many species require very special storage substrates or storage plants: for example, the female of the green damsel only sticks the eggs into the leaves of the crab claw Stratiotes aloides , and many bog dragonflies are bound to the presence of peat moss ( Sphagnum spp.).
In almost all species, so-called prolarvae hatch from the eggs, which differ significantly in morphology from the later larvae. They are usually longer and their legs are not ready for use. The first molt then occurs either in the first few seconds or in the first hours after hatching.
In the water, the larvae are well-adapted predators and, as the most effective organ for this way of life, have a typical trap mask , which is folded under the head when it is at rest. If a potential victim is within reach, this clawed instrument pops out and the prey is grabbed. Dragonflies (Zygoptera) prefer mosquito larvae and small crustaceans such as the river flea shrimp ( Gammarus spp.) As prey . Larvae of the dragonfly (Anisoptera) hunt correspondingly larger prey such as small tadpoles or insects and their larvae.
Dragonfly larvae have two different techniques for breathing underwater, which means that they can be distinguished at first glance: The small dragonflies have three leaf-shaped tracheal gills at their rear end , with which they can absorb oxygen from the water. Large dragonflies, on the other hand, have no visible gills, these are shifted into the rectum ( rectal gills ). The oxygen is absorbed by a special tissue in the rectum.
The duration of the larval life of a dragonfly generally exceeds that of the resulting imago : The span that individual species spend as larva in the water in Central Europe ranges from around three months ( e.g. early darter Sympetrum fonscolombii , summer generation) to five Years ( source maiden , genus Cordulegaster ). A year or two year larval development is the most common case. The animals go through more than ten continuously growing larval stages, each of which ends with a molt.
Towards the end of the last larval stage, the animal leaves the water in order to anchor itself vertically to vertical structures for hatching (emergence). An exception are the river maidens (Gomphidae), which often hatch in a horizontal position on pebbles or the bare ground. The spectrum of emergence sites ranges from roots, stones or rocks, bushes and trees to anthropogenic structures such as bridge piers or boat houses. Most often, however, the larvae seek out the stems or leaves of bank or water plants or reeds to hatch.
The distance covered to emergence is sometimes quite considerable. In the case of falcon dragonflies (Corduliidae) and spring damsel (Cordulegastridae) in particular , distances of a few to many meters have been documented that the larvae covered on their way to a suitable place to hatch - in one case ( Zweifleck Epitheca bimaculata , according to Heidemann & Seidenbusch 1992) even more than a hundred meters.
As a rule, however, they hatch in close proximity to the water. This is where the adult insect ( imago ) hatches from the larval shell, which remains as an exuvia . In almost all cases, the corresponding species in European dragonflies can be determined without any problems on the basis of the exuvia.
The lifespan of the adult animals averages about six to eight weeks for most species. Some species only live about two weeks. The longest lifespan as an adult dragonfly in Central Europe are the winter dragonflies (genus Sympecma ), which overwinter as an adult and thus live ten to eleven months. However, their active life is only about four to six months, as they mostly survive the winter in cold rigidity.
Evolution and systematics
Various dragonfly ancestors are known from the Upper Carboniferous . These animals are known as Protodonata and the most famous representatives include the giant dragonflies (Fam. Meganeuridae) Meganeura monyi with a wingspan of up to 70 and Meganeuropsis permiana with a wingspan of up to 72 centimeters . Even more primitive dragonflies have come down to us from the same period (e.g. from the site in the brickworks hall in Hagen), which are placed in a separate order of Geroptera, they had a rudimentary third pair of wings on the prothorax. The ancient, plesiomorphic features of these orders include: end of the abdomen with terminal filum and cerci (as in modern mayflies), paired penis (also). Probably the animals deposited still free spermatophores like the recent "urine insects" ( little fish and rock jumpers ). At the same time, anatomically more modern, smaller animals that are more closely related to modern dragonflies also lived.
On the Falkland Islands representatives of a group from the Triassic and Cretaceous were found , which were originally thought to be the ancestors of the dragonflies and called Protozygoptera . The Protanisoptera found in Siberia and Australia from the same period were thought to be the ancestors of the dragonflies. The Archizygoptera and the Triadophlebiomorpha are also not included in today's taxa . These animals and also those of the following epochs only reached body sizes of six to a maximum of 20 centimeters and thus corresponded in size to today's species. These groups are all representatives of the root groups of today's dragonflies, ie extinct lateral lines of the modern order, collectively referred to as "Panodonata". The most likely sister group of modern dragonflies is the extinct family Tarsophlebiidae from the Jura . There are also well-preserved fossil dragonfly larvae from the Cretaceous period, which in their morphology are already very similar to those of today. B. they already have a well-trained catch mask. According to the fossil record, the larval type with three gill leaflets (as in today's Zygoptera) is more original than the one with an anal pyramid. The changes in the structure and probably also in the way of life of the dragonflies were only minimal in the last 150 million years.
The dragonflies are divided into three subgroups, which are predominantly viewed as monophyletic groups . According to some taxonomists, however , the dragonflies are not a natural group ( monophylum ), but a combination of several basal dragonflies taxa.
The damselfly (Zygoptera, about 2700 species) as the ancestral species of dragonflies equal pairs of wings, which for most families - an exception for form. B. the Lestidae - are folded back over the body when at rest, and their eyes are wide apart. Another characteristic of this taxon is that the larvae are equipped with three tracheal gill leaflets at the end of the abdomen.
The primeval dragonflies (Anisozygoptera or Epiophlebioptera) only exist in three species in the Himalayas , as well as in China and Japan . They differ from the large dragonflies in the specific formation of the pedicellus , the antennae and the presence of a stridulation organ on the abdomen.
In the large dragonflies (Anisoptera, about 2900 species), the pairs of wings are unevenly large and protrude laterally from the body when at rest. In addition, the dorsal flight muscles are reduced and the animals have a specially designed copulatory apparatus ( penis ).
The original dragonflies and large dragonflies are grouped together as Epiprocta. Common features are the enlarged and closely spaced eyes, the equipment with gripping pliers on the abdomen of the males ( epiproct ) and the development of rectal gills.
A systematic list of the species in Europe can be found under systematics of dragonflies .
The origin of the name "dragonflies" was unclear for a long time. The name was introduced by Carl von Linné , who referred to the group as "Libellula" without explaining this in more detail. The actual source of the name was not discovered until the 1950s. It comes from the work Universae aquatilium Historiae pars altera, cum veris eorum imaginibus by Guillaume Rondelet (1555, "Complete investigation of aquatic life, part 2, with their truthful illustrations"), in which the following is written in chapter 39:
“Insectum hoc libellam fluviatilem libuit appellare, a similitudine quae illi est cum fabrili instrumento et cum Libella marina. Haec bestiola parva est admodum T, literae figuram referens, pedes ternos utrinque habet, Cauda in tres appendices desinit, quae viridi sunt colore, iisdem et pedibus natat. "
“It was popular to name this insect the river dragonella because of the resemblance it bears to the artisan's tool and the sea dragonella. This little animal pretty much forms a T, the shape of which it reproduces; it has three legs on either side, the tail ends in three appendages ( sic !), which are green in color. It swims with these and the feet. "
As can be seen from the attached illustration, Guillaume Rondelet describes the larva of a dragonfly in these lines and suggests naming it libella fluviatilis ("river dragonfly") because it resembles an animal called libella marina (translated here as "sea dragonfly"). He had discussed this animal in Chapter 13:
“Gaza Ζύγαιναν libellam interpretatur. Est autem libella fabrorum lignarorium caementariorumque instrumentum, quo […] rerum in plano positarum aequilibrium siuc libramentum et neutram in partem propendens situs exigitur. [...] Libella igitur ligno transverso constat, in huius medio aliud erectum est, e cuius summo filum annexo plumbo demittitur. Hanc figuram piscis iste capite transverso et reliquo corpore in huius medio sito apte refert, quamobrem libella merito dicitur. ”
“Gaza translates ΖΥΓΑΙΝΑ with Libella. A Libella, however, is a tool used by carpenters and bricklayers, with which ... the horizontal position of objects lying flat is checked. […] A dragonfly therefore consists of a transverse bar, on the center of which another bar stands vertically, from whose upper edge a thread with a lead weight hangs down. This shape is appropriately reproduced by the fish with its transverse head and the rest of the body in the middle; therefore it is rightly called Libella. "
From the illustration below the chapter heading it can be clearly seen that the text deals with the hammerhead shark , which is referred to in the title with the Greek name Zygaena ( Latinized from ancient Greek Ζύγαινα Zygaina ; German roughly: "Jochfisch"). According to Rondelet, the Latin name based on the comparison with a scale goes back to Theodorus Gaza , who, among other things, translated the natural history works of Aristotle into Latin.
Libella is actually the diminutive of Latin libra ("scales"); later it was mainly used torefer to spirit levels. Even today a special measuring device, also on spirit levels, is also known as a dragonfly .
Before the name “dragonflies” became established, the names “water maidens”, “grinders” or “eye glasses” were common for these insects.
In 2001 the flat-bellied dragonfly ( Libellula depressa ) was voted Insect of the Year in Germany . This decision was justified by the fact that the conspicuous and widespread species is representative of all dragonflies (Odonata) and is intended to draw attention to their endangerment in Germany. The main danger is the increasing pollution and draining of many bodies of water that are used by dragonfly larvae as a habitat . The result: two thirds of the around 80 native species are endangered, and 20 percent are even threatened with extinction. Since it is not possible for most laypeople to differentiate between species, all dragonfly species in Germany and most of the neighboring countries are under species protection , so only empty shedding shirts (exuvia) may be collected.
Dragonflies and people
Contrary to popular belief, dragonflies are non-toxic and cannot sting, so they are completely harmless to humans. Old names such as “devil's needle”, “eye borer” or “horse death” came about through this misconception and earned the dragonflies a bad reputation. When a captured, held dragonfly bites a person's finger, it can be felt, but is usually not painful. By themselves, dragonflies never attack people, but are usually shy and flee. However, some large species such as the blue-green mermaid sometimes approach curiously to observe the "territory intruder" humans. They remain standing in the air by shaking flight . Some misinterpret this as an attack.
Dragonflies have a number of popular names that can be traced back to their use in mythology and popular belief . In Germanic mythology, dragonflies were assigned to the goddess Freya or Frigg and were sacred. This pagan worship was reversed by missionaries together with the meaning of Friday , which is dedicated to Freya , the dragonflies became "devil needles", "devil bolts" or "eyeglasses" and Friday became the unlucky day. The fear of dragonflies that was widespread at the time has persisted to this day through the idea that dragonflies could sting. In Luxembourg the name Siwestécher 'Siebenstecher' is used, which goes back to the belief that seven dragonfly stings can kill a person.
In the Japanese creation myth of the island kingdom described in the two oldest chronicles of Japan, Kojiki and Nihongi , the largest island of Honshū is referred to as Ō-yamato-toyo-aki-zu-shima (Kojiki: 大 倭 豊 秋 津 島 , Nihongi: 大 日本 豊 秋 津 洲 , German "Great Yamato Fertile Dragonfly Island"). The name is said to go back to the first Tennō , Jimmu , who compared the shape of Japan ("Great Yamato") with a dragonfly drinking with its tail. The dragonfly was a symbol of imperial power in early Japan. In popular belief, it was regarded as the spirit of the rice plant and a harbinger of a fertile autumn - the part of the name 豊 秋 can be read as “fertile autumn”. In Japanese poetry, “dragonfly island ” ( Akitsu-shima or Akizu-shima ) is a poetic name for Japan and the dragonfly itself is a popular motif.
The dragonfly can also be found regularly in literature, for example in Heinrich Heine's poem Die Libelle , in various works by Annette von Droste-Hülshoff or in Heinz Erhardt's humorous poem Die Libelle , in which he wrote:
don't fly so fast!
Think of the dangers that
await you [...] "
Especially in modern cartoon series, starting with Maya the Bee and Antz up to various Japanese mangas , the dragonfly is used as a flying device due to its flying skills, in others it represents the design for futuristic-looking spaceships in the shape of a dragonfly (e.g. in Captain Future or Lexx ). Also noteworthy is the several-minute opening credits of the Hollywood science fiction comedy Men in Black , which was designed entirely from the perspective of a hunting dragonfly.
In the course of the “ Most Beautiful German Word ” poll , which was organized by the Goethe Society, “Libelle” was voted the most beautiful word in the “Children's Suggestions” category in 2004.
A cigarette paper booklet from Altesse KG made from cigarette paper from Olleschau Papier Industrie AG had a dragonfly as its trademark. The outspread wings symbolize the thinness of the paper. Libelle Verlag, named after the animal, has existed as an independent book publisher since 1979 .
The Unterspreewald (Brandenburg) office leads u. a. a dragonfly in the coat of arms.
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