The sun is burning from the sky, the meadows are withered, only the irrigated corn is exotic in the heat, and the Sasbach, which is more of a small stream here, meanders through it. In the water stands the biologist and dragonfly specialist Franz-Josef Schiel, who is currently looking for dragonflies (Odonata) in rubber boots and with a landing net in his hand. He does not have to wait long, close above the water, on the edge on the reeds or on the dry grasses; as a layman, one has the impression that it is just teeming with dragonflies here. As fast as an arrow, they fly over the water, stand in the air, change direction, and then sit down briefly – rarely long enough for a photo.
Drabs are considered the perfect air animals and are the fastest flying insects. You can move your four wings independently of each other with your own muscle. As a result, they fly forward, backwards, backwards, to the right and left or like a helicopter. In addition, simply use the thermals and sail leisurely there. "Drabs can accelerate from zero to 15 kilometers per hour in 0.3 seconds and reach flight speeds of up to 40 kilometers per hour," explains Schiel. »Libelle eyes have a five -time resolution than the human eye and can take up to 300 frames per second. All of these properties together make dragonflies into the best air hunters among insects, and their enemies also have little chance of catching them. ”The doctor of biologist has been dealing with dragonflies for almost 30 years, which he has been doing for himself in 1996 through his diploma thesis in Freiburg discovered, "a manageable group that could be familiarized well".
Hard times for dragonflies
Schiel is a founding and board member of the Libellen protective group in Baden-Württemberg, co-founder and partner of the Institute for Nature Conservation and Landscape Analysis (Inula), co-author of the standard work on the dragonflies of Baden-Württemberg as well as dragonfly explaners and conductors.
Together with his colleague Holger Hunger, he described a new type of dragonfly, Protallagma Hoffmannii ten years ago during a scientific excursion in Peru. The dragonflace type Leptogomphus Schieli, newly discovered in a state of Malaysia, is named after him as well as Pseudagrion Schieli, a slanker that was found in the Philippines in 2011. Incidentally, he has this in common with Sir David Attenborough, whose favorite insects are the dragonflies and who, in honor of his 90th birthday, also became the namesake for a dragonfly, Acisoma Attenboroughi, who is at home in Madagascar.
All dragonflies are now under protection and, like other insects, are struggling with the changes in their habitats. "Of the 81 native species, 35 are on the Red List and warning list of endangered insects," explains Schiel. Things are not looking much better worldwide, as the IUCN (International Union for Conservation of Nature) wrote in the updated Red List in December 2021. "The destruction of wetlands is driving the decline of dragonflies worldwide," according to the first global assessment of these species in the update of the IUCN Red List of Endangered Species.
"Your decline is symptomatic of the widespread loss of swamps and freely flowing rivers in which you occur, which is mainly due to the spread of non -sustainable agriculture and urbanization around the world," the IUCN continues. The evaluation of the global dragonflies and small drivers shows that 16 percent of 6016 species are threatened with extinction because their freshwater breeding places are increasingly worse. In southern and Southeast Asia, more than a quarter of all types are threatened, mainly by draining wetlands and clearing of rainforests to create space for agricultural cultures such as palm oil plantations.
Their habitat is being destroyed worldwide
In Central and South America, the clearing of forests for residential and commercial buildings is the main cause of the decline in the dragonflies. Pesticides, other pollutants and climate change would be a growing threat to species in all regions of the world and are the greatest danger to dragonflies in North America and Europe. "Libelles are highly sensitive indicators for the state of fresh water ecosystems, and this first global evaluation finally shows the extent of their decline," says Dr. Viola Clausnitzer, co -chair of the IUCN SSC Dragonfly Specialist Group.
"Dragonflies are therefore also among the species that are examined in environmental impact assessments as part of intervention projects, there are species protection programs, and ten native species are included in the European Fauna-Flora-Habitat Directive and are therefore strictly protected," explains Franz-Josef Schiel, who also works as an expert himself. A few other species - Alpine mosaic damselfly, High Moor mosaic damselfly, Late Ruby Damselfly, Alpine Emerald Damselfly, Eastern Blue Arrow, Dwarf damselfly - are also "strictly" protected in Germany.
Climate change also troubles dragonflies
In addition to the loss of their habitats, climate change is creating problems for the dragonflies. "We have an increase in southern species here; thanks to the many years of research, we can document this in Baden-Württemberg in real time, so to speak," explains Schiel. Heat-loving and heat-demanding species are increasing, conversely, those for whom it is now too hot here are disappearing, the Alpine mosaic maiden has now become extinct with us.
The same can be seen in other federal states. The Speer Azurfer used to be a common way in Lower Saxony, now it has almost completely disappeared there. And of course, the moor species such as the Alpine emerald libelle have general problems, since the bogs dry out, according to Schiel. Larvae of these specialized bog types could survive a certain dry season, but at some point it was over. And so it goes on, because "Tümpel falls too quickly in the meantime in the spring, so that species such as spotted Heidelibelle, shiny binsjungfer or small pechlibelle, the dragonfly of 2022, cannot complete their development".
The changes in the rivers are now dramatic. Breaks fall dry, water quality, flow speed and of course the temperature change in larger waters. These consequences of climate change are very frustrating for Schiel, because a lot has been done for water quality since the 2000s. It had improved a lot, which was also possible for the dragonflies. But there is little to do against the effects of climate change, and he assumes that this is why species would disappear in Baden-Württemberg and elsewhere. Although many European species had a large distribution area compared to those in tropical rainforests and could therefore also dodge, "but you want to get biodiversity on site," emphasizes the biologist.
Data analyses by a working group led by Diana E. Bowler from the German Centre for Integrative Biodiversity Research (iDiv) over the past 35 years confirm these observations by Schiel. There, too, one comes to the conclusion that climate change, on the one hand, is a key role for the spread of many dragonfly species, but on the other hand, one can observe a considerable number of declining cold-adapted "loser species".
The decline can also be seen on the small Sasbach in Baden, because you can see many dragonflies, but there are only a few different ways. "There is a banded splendor there, a blue feather body at the back." Franz-Josef Schiel suddenly swings the net and I can finally admire the dragonfly up close. It is not big, mostly turquoise with black longitudinal strips, her eyes sit on the right and left of the head. "It is one of the small drivers," says Schiel. On the one hand, you can see them on the side of the eyes and on the other hand by the wings that folded behind your back and almost equally designed. In contrast, the eyes of the large -fashioned poets stand together and they keep their unequal wings spread out in rest.
Rabid males, sperm competition and catchmask
On the Sasbach, the blue feather libel is still quite common at the moment, because you can even see a mating wheel in the corridor along the stream and on a reeds on the edge of the water, something that does not exist in this form in other insects.
"The dragonfly males can be quite rabid, at the reproductive waters it is often the case that you only see males and no females there, because if a female lets herself be seen, she is immediately forced to mate," comments Schiel. The male first grabs the female behind the head with the pincers of his abdomen and a dragonfly tandem is created. Then the female bends her abdomen forward, the animals form the mating wheel and sperm transfer occurs.
»The phenomenon of sperm competition was also discovered for the first time at Libellen. Males have a kind of brush with which they can scrape out the sperm of the predecessor from the female seed pocket, «explains Franz-Josef Schiel. This is also the reason why many males would not let the females out of their eyes until the egg laying. The actual fertilization only takes place in the case of egg laying, depending on the species in tandem or alone, but under guard by the male.
A bit monstrous
The special features of the dragonflies continue with their larvae. They develop in the water and are powerful predators. Your lower lip is converted into a fishing mask, so that you can take a quick fit and capture water insects. A resemblance to aliens in sciecefiction films is not entirely dismissed.
Depending on the dragonfly species, it can take up to five years for the finished flying insect to hatch after several larval stages. The adult dragonfly larva climbs out of the water on plant stems and the finished insect hatches from the chitinous carapace, which remains hanging on the stems, the so-called exuviae. "They are characteristic of every dragonfly and are also used to determine the species," says Schiel. After hatching, the finished dragonflies remain seated until the spread wings are completely unfolded and hardened, only then does the "aerial part" of their life begin, which usually lasts only a few weeks.
There were dragonfly -like insects around 300 million years ago. The ancestors of our dragonflies today, the Meganeura, had an impressive wing span of up to 75 centimeters, they flew at 70 kilometers per hour and were able to climb in the air at five meters per second. The meganeura were also hunters. They had sharp mouth tools and tips claws and their prey had little chance of escaping.
Dragonflies as a model for drones
Today's dragonflies became significantly smaller compared to that time, but can still come to around 20 centimeters. »However, many species are smaller. The ›Gnom among the domestic dragonflies‹ is only 26 millimeters in size, «says Schiel. This tiny is the dwarf globe, an extremely rare way that has declined sharply in the past decades. Here, too, climate change and pollutant entries led to their sensitive moor habitats to a decline in populations. As early as 1837, these "insects on the Riedgras of large moor holes and on bubbles overgrown with bits" were described.
While the dragonflies have shrank significantly in the last 300 million years, possibly due to the falling oxygen content of the air and the appearance of child competitors and predators such as flugreptiles and flight dinosaurs, their "blueprint" has hardly changed. As now, their flight skills were exceptional, they have developed over millions of years to ensure their survival. Your special skills are not just the biologists today.
A team of doctoral students from the University of South Australia (Unisa) under the direction of the Professor of Sensor systems, Javaan Chahl, spent part of the Covid 19-Lockdown 2020 designing and testing important parts of a drone inspired by dragonflies. It could successfully reproduce the exceptional capabilities of the insect in floating, cruising and aerobatics. In recent years, drones have become increasingly common and fulfill a wide variety of functions, but compared to the dragonfly and other flying insects, they are rather primitive and consume a lot of energy.
The UniSA team modeled the dragonfly's unique body shape and aerodynamic properties and reconstructed 3-D images of the wings. "Dragonfly wings are long, light and stiff with a high ratio of lift to drag, which gives them superior aerodynamic performance. Her long abdomen, which makes up about 35 percent of her body weight, has also evolved to serve many purposes. It houses the digestive tract, is involved in reproduction and helps with balance, stability and maneuverability. The abdomen plays a decisive role in their ability to fly," Chahl said in a statement from UniSA. Through their experiments, the scientists around Chahl come to the realization that an optimal flapping-winged drone could look a little like an abstract dragonfly.
