How far can a dragonfly fly
In the 16th century, a French researcher found that the larvae of the dragonfly looked like a hammerhead shark; At that time the scientists referred to this with the Latin name because of its head shape libella (= Spirit level; this device had the shape of a T at the time). Carl von Linné, the founder of scientific naming, made the diminutive libellula to denote the genus.
How long have dragonflies existed?
The currently oldest fossils of dragonflies come from slate deposits of the Upper Carboniferous (coal age) in the Ruhr area. They are 325 million years old. The dragonflies are among the oldest recorded flying insects.
How many species of dragonflies are there?
Today it is assumed that there are over 5000 species, of which only about 80 occur in Germany. 53 species have been identified in the Bremen area.
How big can dragonflies get?
Dragonflies with a wingspan of 75 cm are known from the Permian Age (280-230 million years ago). The record among today's dragonflies is held by a tropical species with a wingspan of up to 19 cm and a length of 16 cm; the largest native species reach a wingspan of 11 cm and a length of 8 cm. (For comparison: the smallest species in this country measures 1.9-2.2 cm and spans approx. 2.5 cm).
What role do dragonflies play in the ecosystem?
Both larvae and adult dragonflies are great hunters. Studies in India have shown that a dragonfly larva can devour over 130 mosquito larvae per day; how many flying insects (especially flies and mosquitoes) an adult dragonfly hunts daily is not so easy to determine; however, it is clear that a considerable amount of food is required to provide the necessary energy for the large animals.
Conversely, the dragonflies serve as prey for numerous other hunters. It can be assumed that 95% of the animals hatched from the egg perish without having reproduced. The few who got away have to take care of the conservation of the species.
The dragonflies as a genus are important links in the food chain of the overall ecological system on the one hand for regulating the population of smaller flying insects and on the other hand as a food source for other species.
Are dragonflies dangerous?
The vernacular said dragonflies did bad things: they could sting dangerously or even sew up the eyes of someone who fell asleep in the open air. Hence names like "Satan's Bolt" or "Devil's Needle". In reality, dragonflies are completely harmless except for their prey insects. It is true that the females of many dragonfly species have an ovipositor with which they lay their eggs in plants or in the ground. But it is only used for this one purpose. So, unlike the poisonous defensive sting of bees and wasps, it is not at all dangerous.
Why do dragonflies seem threatening to many people?
It has been found that large, staring eyes make a dangerous impression on people. That makes the look from the lidless eye of a snake frightening, for example, while a lizard that can blink seems likable to us. Since the eyes stand out due to their size and color, especially in large dragonflies, the animals look threatening. (By the way: even the masks of evil demons among primitive peoples have huge rigid eyes).
How do you differentiate between females and males in dragonflies?
First of all, the sexes of the dragonflies differ fundamentally in terms of color. Usually the females are more inconspicuous. Only more precise knowledge helps to differentiate here.
In addition, there are clear characteristics when you can see the animals up close:
The females have a laying apparatus on the underside almost at the very end of the abdomen, which is designed as an ovipositor in species that prick their eggs in plants or in the ground.
The males have a mating organ on the second abdominal ring near the breast on the underside, which forms a small hump, but which is not noticeable from a distance. In addition, males do not only have 2 abdominal appendages like females, but 3 (large dragonflies) or 4 (small dragonflies). With them they cling to the neck of the females when mating. (A dragonfly that clings to someone else's neck with these attachments during a wedding flight can only be male).
How many eggs do dragonflies lay?
The number of eggs in large dragonflies is generally greater than in small dragonflies; but it also depends on how the eggs are laid. Species that pierce their eggs into plants need fewer eggs to maintain their species than those that drop their eggs in free flight over bodies of water. In the case of our native dragonfly species, the range extends from the bat azur damsel (small dragonfly; deposited in plants) with approx. 80 eggs to the two-spot (large dragonfly; shed) with up to 2000 eggs per female.
Why do dragonfly larvae have to molt 7-15 times before the animal is adult?
The chitinous skin of the insect larvae does not grow with them. So after a while, if the animal has fed well, the chitin shell becomes too tight: it literally bursts out of the skin. A new, still soft, stretchable skin has already formed underneath, but it will firm up in a short time. How long it takes from one molt to the next one depends on the food available. How many molts an animal has to go through in total is determined in the genome for each species.
The dragonfly larva as a hunter
Anyone who observes a dragonfly larva would hardly believe that it will develop into such a nimble and agile air hunter because the larva is sluggish and sluggish. This is because it has to assert itself under completely different conditions than the adult animal: Moving forward quickly under water requires a comparatively high amount of energy. It is therefore an adaptation to the habitat when dragonfly larvae hunt their prey by ambushing and stalking. However, the hunter then has to grab her prey at lightning speed and overwhelm it. For this purpose, the lower jaw of the dragonfly larvae is transformed into a strange "trap mask" with which it grabs its prey as soon as it is within reach.
How do dragonfly larvae move?
Dragonfly larvae are sneaky hunters, so unlike the adult animals, they are easy to walk. But in order to cover longer distances quickly, e.g. on the run, they swim. The larvae of small dragonflies swim with meandering movements (similar to an eel), those of large dragonflies use rocket technology, so to speak. Usually they pump water in and out through the abdomen opening to supply the gills in the rectum with oxygen that is dissolved in the water. To swim, let yourself go and suddenly squeeze all the water out of your abdomen. This will cause them to shoot forward a little. This process can be repeated several times.
Why do you find dragonflies far from the water?
With their larval development and egg-laying, dragonflies are bound to water, but after hatching, the animals still need a development time before they are sexually mature. During this time they sometimes move far away from their slip waters, so that they even appear in large cities. This ensures that new bodies of water are also colonized by dragonflies and that the animals do not compete too much on their hatching bodies.
There are real hiking specialists among the dragonflies. Some species invade every year from the Mediterranean to southern England or even to southern Germany. They can even reproduce there. The animals hatched here migrate back to the warm south in autumn, as has been observed on passes of the Alps and Pyrenees. These regular migrations are similar to the bird migration with the difference that the individual animal does not live long enough to move there and back. However, relatively little research has been carried out into these hiking trails.
Flocks of dragonflies
The migration from the slip waters described above is roughly evenly directed in all directions. In the case of mass reproduction, however, some species behave differently (e.g. four-spot and darter): They then form swarms similar to migratory locusts and thus move away together over long distances. In the best case scenario, this allows the species to develop additional settlement areas. In the last century, a swarm of four-spot dragonflies in Germany was estimated at 2.5 million animals, in 1974 the observation station Randecker Maar (Swabian Alb) identified a swarm of darter dragonflies on a south course, which they moved at 360,000 dragonflies per hour and kilometer Width calculated.
Flight performance of dragonflies
Amazing flight performances have become known from dragonflies. Dragonflies have been found on the high seas more than 530 km from the nearest land. It has been observed that dragonflies from Libya or southern Italy reached Iceland within 4 days with a favorable air current or that a swarm of dragonflies crossed southern Sweden within 12 hours.
Exact measurements of the airspeed are hardly available. However, speeds of around 100 km / h are ascribed to the dragonflies. In America, the plane measured 90 miles per hour (approx. 135 km / h), but it is unclear what wind conditions prevailed.
Why do dragonflies rarely fly before 10 a.m.?
Like all insects, dragonflies are cold-blooded, i.e. they adapt to the outside temperature. So in the cold night, dragonflies get clammy and clumsy. Only when they are warmed up by the warmth of the day are they ready for hunting. You can therefore often see dragonflies basking in the sun to soak up warmth. But dragonflies cannot tolerate too much heat any more than other living things. On particularly hot days you can therefore observe dragonflies, which stretch their abdomen exactly towards the sun in order to offer their rays as little attack surface as possible.
Why don't dragonflies hum or humming when they fly?
The humming noise of other insects occurs because they make the air vibrate by flapping their wings. The faster the wing beat, the higher the pitch. Bumblebees grumble with their comparatively slow wing beat (120 - 160 per second), mosquitoes buzz (approx. 600 per second). Dragonflies have a rather slow wing beat (only about 20-30 per second). Therefore, a human does not normally hear any flight noise from them, except for a crackling of dragonflies, which only occurs when the hind wings rub against the forewings during flight maneuvers.
Why are dragonfly eyes made up of up to 30,000 individual eyes?
Dragonflies are fast-flying hunters whose prey also flies very skillfully. So you have to capture your target quickly and precisely and keep an eye on it and avoid obstacles in good time. To do this, they must be able to see much better than honey bees, for example, which do not fly nearly as fast and whose targets, the flowers, are stationary.
But why do dragonflies have so many individual eyes in their complex eyes? Unlike the human eye, which with its lens can continuously adjust the visual acuity to different distances, the individual compound eye of an insect with its rigid lens only shows a sharp image at a certain distance. Only a complex eye made up of numerous individual eyes allows precise orientation.
Incidentally, the upper part of the complex eyes of the dragonflies is more focused on distance vision, the lower part on near vision.
How do dragonflies hibernate?
The adult dragonflies usually only live for about 14 days, at most 6 - 9 weeks. Therefore, only larvae overwinter (from species that fly in early summer or that have a perennial larval development) or eggs (from species that lay eggs in autumn). Only two European species, the winter dragonflies, survive the winter as adults. You can therefore live to be 11 months.
Extreme living conditions (European species)
In Europe, dragonflies can be found in the mountains up to an altitude of 2200 m. 8 species can also exist north of the Arctic Circle. The adult animals (imagines) of the winter dragonfly survive more than -15 ° C. The eggs of the willow jumgfer can even endure more than -30 ° C. The larvae of the four-spot dragonfly can even develop in brackish water. The larvae of the flat-bellied dragonfly survive the desiccation of their home waters for over 7 weeks.
Do dragonflies of different species also mate with each other?
Dragonflies of different species do not mate successfully, even if they are closely related. The males' abdominal appendages, with which they cling to the females to mate, are shaped differently depending on the species. The "mounts" in the neck of the females are designed accordingly. Only the "correct" grip of a male of the same species triggers mating behavior in the females (one speaks of a key-lock system). Mating errors are avoided in this way.
Why are all dragonflies under conservation?
In fact, there are dragonflies that are great at adapting to changing environmental conditions and are not currently threatened. But this only applies to about a third of our species. The other species, however, some of which can only be distinguished from these robust survivors by a specialist in precise studies, are in some cases highly specialized and threatened with extinction due to even minor changes in their habitat. Here's an example: Until a few years ago, the green maid of the mosaic was common everywhere in Blockland and St. Jürgenland. This species only lays its eggs in the crab claws, which formed large populations there in the drainage ditches. This plant does not tolerate over-fertilization of the water. Due to the intensive pasture use of this area and the application of liquid manure, so many nutrients got into the waters that crayfish claws are hardly to be found there. As a result, this dragonfly species has also become rare there and, if it continues like this, has little chance of survival in the area mentioned.
How special the requirements dragonflies place on their environment can also be seen from the following observation: When a watercourse about 1 km in length was examined in Schleswig-Holstein, it was found that dragonflies only had eggs on a section of less than 50 meters cast off, although the observers did not notice any particular difference to the remaining sections of the water.
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