Blue-winged demoiselle

from Wikipedia, the free encyclopedia
Blue-winged demoiselle
Blue-winged demoiselle (Calopteryx virgo), male

Blue-winged demoiselle ( Calopteryx virgo ), male

Systematics
Order : Dragonflies (Odonata)
Subordination : Dragonflies (Zygoptera)
Superfamily : Calopterygoidea
Family : Demoiselle (Calopterygidae)
Genre : Calopteryx
Type : Blue-winged demoiselle
Scientific name
Calopteryx virgo
( Linnaeus , 1758)

The blue-winged demoiselle ( Calopteryx virgo ), also known as the common mermaid , is a type of dragonfly from the family of the demoiselle (Calopterygidae) within the small dragonflies . Besides the banded demoiselle ( Calopteryx splendens ), it is the only type of demoiselle in Central Europe and is particularly noticeable because of the blue wings of the male that give it its name.

features

Construction of the adults

female
Males (left) and females of the blue-winged demoiselle

The imago of the blue-winged demoiselle reaches a wingspan of 6.5 to 7 centimeters.

The color of the wings is particularly noticeable in this species. The wings of the males are completely blue-green and those of the females are colored translucent brownish to copper. As with all dragonflies, they are very broad and do not have a stem-like attachment. The wings are also traversed by a dense network of veins and have no wing mark ( pterostigma ). In the females, however, there is a false wing mark, in which there is a denser veining.

For comparison, a male of the banded demoiselle ( C. splendens )

Due to the very clear coloration within the distribution area, there is a risk of confusion only with the banded demoiselle, which is also very similar to this species in its way of life (for this reason it is regularly used for comparisons in the following text). In this case, however, the blue coloration of the males is limited to only part of the wing, about a third of the base is always translucent, and parts of the wing tip are usually colorless. Another distinguishing feature is the underside of the last three abdominal segments, which are yellowish-white in the banded dragonfly and bright red in the blue-winged dragonfly. The body and the wings of the females of the banded demoiselle are metallic-green. However, there is a high risk of confusion between the females of both species, especially in the case of freshly moulted and not yet colored female dragonflies, as well as photographs with flashlight.

Construction of the larvae

The larvae of the blue-winged demoiselle develop over 10 to 12 larval stages , between which a molt takes place. The body length of the animals is very variable and strongly dependent on the environmental conditions, for this reason the comparative body sizes are given in the literature on the basis of the head width. In the final stage ( F-0 stage ) of the larva, this is between 3.5 and 4.6 millimeters and the body weight is around 4 milligrams, slightly below that of the banded demoiselle. Apart from that, the larvae of the dragonfly are difficult to distinguish from one another, the recognizable differences are mainly in the bristling and the expression of the tracheal gills on the abdomen. Compared to other dragonflies, on the other hand, the dragonfly larvae are immediately noticeable due to their significantly shortened central gill leaf.

The build of the larvae shows only a relatively small adaptation to the fast flowing waters of their habitat. The body is not flattened, but very slender and round, the legs are long and have strong claws at the end with which they can hold on to the vegetation. Since they are mainly located in the quieter areas within the body of water, the risk of being drifted with the current is relatively low. If this happens anyway, they stretch their long bodies and legs as far as possible in order to come into contact with the vegetation or the substrate .

distribution

The distribution area of ​​the blue-winged demoiselle includes all of Europe with the exception of the southwestern Iberian Peninsula, the Balearic Islands and Iceland . In the north it extends as far as the Arctic Ocean and thus significantly further north than that of the banded demoiselle. On the North African Mediterranean coast, their southernmost populations can be found in Morocco and Algeria.

The northern limit in Asia follows the 13 ° C July isotherm , so it does not occur in the areas where the average temperature in midsummer falls below 13  ° C , otherwise it is found in the temperate and cool areas across the board Continent with the exception of the desert areas and the high mountains. The most easterly subspecies C. v. japonica is found on the Japanese islands, but it is discussed whether it is a separate species.

Like the banded demoiselle, the blue-winged demoiselle is mainly found in lowlands. Regular finds come from areas up to a maximum height of 980  m , but occasionally they can also be found at heights of up to 1,200 meters, for example in the Alps .

Habitat

Biotope

Magnificent blue-winged dragonfly with folded wings. This resting position is typical for dragonflies

The blue-winged demoiselle lives mainly on small to medium-sized streams and other flowing waters . These are characterized by a relatively low water temperature and a moderate to fast current. The waters must not be too rich in nutrients ( eutrophic ). In the northern part of its range, for example in Norway , it can also be found on medium-sized rivers and in northern Finland even in larger rivers. The waters are mostly in close proximity to forest stands. In contrast to the banded demoiselle, it can even be found on streams within forests and on bog streams and ditches.

Imaginal habitat

The imaginal habitats, i.e. the habitats of adults, largely correspond to those of the banded demoiselle, whereby corresponding larval habitats must be available. Unlike the adults of the banded demoiselle, the blue-winged demoiselle can also be found in forest clearings, but very rarely on the banks of larger still waters. The animals need trees and bushes as resting places, but tall herbaceous plants such as the great nettle ( Urtica dioica ) are often sufficient.

The reproduction habitats correspond to the future larval habitats, they are cool, largely shaded watercourses with a more or less strong current and a natural and vegetated bank structure. These are mainly streams in the meadow and pasture area, rarely they flow through the forest. A distinctive bank vegetation obviously also plays a role as wind protection, as the animals can be blown away by the wind more easily than other dragonfly species due to their wide wings.

Larval habitat

The larvae live in the streams named above and are mainly found on the vegetation in the water, which they have in common with the larvae of the banded demoiselle. You will need the stems and leaves especially in areas with stronger currents to hold on to. On the other hand, they are rarely found in places with little vegetation and on shallow banks or areas with a smooth stone floor. In quieter areas they live between alluvial leaves or on exposed roots of the bank vegetation. They can also be found in underwater plants such as waterweed ( Elodea sp. ), Flooding water crowfoot ( Ranunculus fluitans ) or other plants. They usually stay at depths of a few centimeters to a few decimeters.

Compared to the larvae of the banded demoiselle, the larvae of the blue-winged demoiselle prefer the calmer areas of the water, as a more effective absorption of oxygen from the water is made possible when the current is lower . Only in very rare cases are the larvae found in stagnant water. The substrate of the water is only of minor importance, as the larvae are mainly in the vegetation.

The oxygen supply of the water is an important factor for the occurrence of the blue-winged demoiselle. The larvae react much more sensitively to a lack of oxygen than the larvae of the banded demoiselle, so that the oxygen saturation of the water must be correspondingly high. Waters with high proportions of sediment and digested sludge , in which oxygen is consumed by bacterial degradation processes, are accordingly unsuitable as a habitat for the larvae. Because of this sensitivity, which also affects other factors in aquatic chemistry, the animals can be used as a bio-indicator for assessing the water quality. According to DIN , they are assigned an indication value in the saprobic system of 1.9, which stands for a slightly to moderately polluted water type (β-mesosaprob) and means a water quality class from I to II.

Another central factor for the occurrence of the larvae of the blue-winged demoiselle is the heat balance of the water. Unlike the banded demoiselle, this species prefers the cooler and more shady areas of the water. A summer average of 13 to 18 ° C is given as the optimal temperature. At temperatures above 22 ° C, damage to the larvae and, above all, a reduced hatching rate from the eggs were often found. The main reason, however, is not the temperature, but the associated reduced capacity of the water to absorb oxygen and the associated lower oxygen content. However, individual populations can get used to permanently higher temperatures.

Way of life

Flight times

Male before departure

The first adults of the dragonflies appear from the end of April to the end of September, depending on the weather. The main hatching time is from the end of May to the end of June. The emergence , i.e. the transformation of the larvae into adults and the associated leaving the water, does not take place synchronously and lasts for the entire season until around mid-July. After leaving the larval shell ( exuvia ), the newly hatched dragonflies spend the first time in the vegetation surrounding the water until they are completely colored. This ripening period usually lasts about 10 days, after which they return to the water. The adult animals only live one season, with a lifespan of around 40 to 50 days.

During the day, the males can be found in sunlit waters early in the morning (in Central Europe between 7:00 a.m. and 9:00 a.m.), and they always stay in the areas that are directly illuminated. In shady waters, the animals appear later, mostly they bask in the tops of the surrounding vegetation. During the day, females fly over the water in search of suitable oviposition sites, the main activity of both sexes such as hunting, advertising , mating and oviposition takes place in the warm midday hours. In the evening, as in the early morning, the animals sit in sunlit resting places in the vegetation; in these places they also spend the night.

The range of action and thus the distance between the breeding, hunting and resting areas is between 20 and 100 meters for the males and is therefore very small, whereas for the females, migration distances of up to four kilometers per day have been observed.

behavior

As with the banded demoiselle, there is also a pronounced territorial behavior of the sexually mature males in the blue-winged demoiselle . These occupy daytime territories that they defend against other males. The defense consists mostly in threatening gestures. To do this, they spread their wings and thus display them in a clearly visible way. There are also threatening flights and, in rare cases, aerial battles between rival males. Optimal territories correspond to the optimal egg-laying locations for the females and are usually characterized by an increased current and a suitable egg-laying substrate in the potential breeding waters. The size of the districts and their distance from one another depends on the density of the population and the conditions in the body of water and can be between several meters and a few decimeters. Males who cannot occupy any territories stay in the vegetation of the bank and try to mate with incoming females or to occupy territories that become free. Especially when there are only a few males, the defense of the territory is very aggressive, but with a higher number of competing males the aggression decreases significantly.

The males sit in their territories mostly in exposed places in the vegetation that extends over the water, sometimes also on vegetation pads or stones in the middle of the water. This seat attendant also represents the center of the area. They focus their gaze primarily on the center of the water and show a behavior that is known as “wingclapping”, in which the wings are quickly flapped down and slowly raised again. It is believed that it is primarily used for communication, but it also supports ventilation in the thorax and therefore probably also plays a role in the thermoregulation of the animals.

Mating and laying eggs

Magnificent blue-winged dragonflies in the pairing wheel
Females laying eggs

The mating takes place in a way that is typical for the genus Calopteryx and is preceded by a conspicuous advertising behavior. The females fly over the water, always looking for suitable places to lay their eggs. They fly through the territories of the males. The males, which females recognize by the light reflections of the moving wings, fly towards them as soon as they have flown over the territory boundary. They use a conspicuous hovering flight , which is only shown during courtship , and present the underside of their high abdomen. The last three segments of the same are clearly lighter and are referred to as the “lantern” that is presented. In this way, the male guides the female to the egg-laying places ("pointing flight") and circles around it on the water surface as soon as it has settled. This is again followed by a phase of soaring flight. Only when the female remains seated and thus signals that she is ready to mate does mating take place. To do this, the male sits on the wings of the female and begins copulation , which can last between 40 seconds and over 5 minutes, whereby the animals can also sit on the vegetation as a mating wheel .

After mating, the male separates from the female again and shows her the egg-laying site again, the female remains sitting with her abdomen hanging down for a few seconds (“post copulatory rest”) and then follows the male. The eggs are laid in the stems of the aquatic plants in the area of ​​the water level and below, whereby the female can submerge for up to 90 minutes. It climb in (unlike almost all other species of dragonflies) head down the stem down and pierces the eggs with the egg-laying apparatus ( ovipositor ) almost vertically into the stalks one. During the egg-laying above the water surface, the female is defended against other males by the male. Both sexes mate several times a day and over several weeks until they die.

Larval development and lifestyle of the larvae

The eggs in which the embryos develop are about 1.2 millimeters long on average and have a spindle-shaped structure that is about 0.2 millimeters wide. At the pointed end, like other dragonflies, there is a hole structure ( micropylene apparatus ) with four holes that allow the male's sperm to penetrate. In addition, the egg of the banded dragonfly has a funnel-like appendix of unknown function at the front end, which protrudes outward from the plant stem when the egg is pierced. The color of the eggs changes from a light yellow in the freshly laid egg through a yellow-brown to a red-brown in the older egg.

The dragonfly's embryonic development takes place within the egg. This was first described for the blue-winged demoiselle in 1869, and it was the first description of the embryonic development of an insect at all. From the outside, the progress of the development can be recognized by a slight change in length and a change in shape. The upper part of the egg arches slightly, while the lower part becomes concave. The development itself can be divided into three sections:

  1. the primitive development, in which the basic shape of the body develops after fertilization through division of the egg cell
  2. the definitive development with the final formation of the body shape up to the hatching from the egg
  3. the larval development of the hatched larva up to the formation of the winged imago

Embryonic development in the egg can take between 20 days and a month.

The larval development of the blue-winged demoiselle usually takes between six and nine weeks in Central European waters, especially due to the preference for cooler waters, it is usually a little longer than that of the banded demoiselle. At the end of the larval development, there is hibernation and the development is not fully completed until the following year with the metamorphosis to the imago ( univoltine development). The cooler the breeding water, the greater the proportion of larvae that go through two wintering phases and thus have a development phase of almost two years (semivoltine development). Studies have shown that the ratio of univoltine and semivoltine larvae can also change significantly within a body of water and shifts in the direction of univoltine larvae in the course of the body of water and with an increase in water temperature.

Like all dragonfly larvae, these are also predatory. They feed primarily on insect larvae such as those of the black flies , mosquitoes , stone flies and mayflies as well as flea crabs . They defend their seat against other dragonfly larvae, especially those of their own species.

The larvae react much more sensitively to changes in the habitat than those of the banded demoiselle, especially to temperature fluctuations. Even after a few days of undersupply, the mortality rises rapidly, and even after the oxygen conditions are acceptable again, malformations and an increased mortality rate among the affected animals continue long afterwards. This is mainly due to the fact that they absorb oxygen from the water less efficiently. Experiments have shown that even larvae of the banded demoiselle, from which the tracheal gill leaves had been completely removed, are normally still less sensitive to fluctuations in the oxygen supply. The inefficiency of oxygen uptake is compensated for by the choice of habitat, as both colder water and currents increase the absorption capacity.

Hazard and protection

Detail view of a male
Detail view of a female

Since the blue-winged demoiselle, due to its very narrow ecological demands ( stenocia ), especially of the larvae, can only occur in waters that are characterized by a body of water that is little influenced by humans and close to nature, it is very rare in most of its range. Accordingly, it is completely absent in areas around larger cities or around industrial conurbations, and it is also only rarely found in regions with high levels of agricultural use. In accordance with this situation, it is classified as endangered in the Red List (1998) in Germany , and in some federal states it is threatened with extinction. The situation is similar in Austria, Switzerland and other Central European countries.

The factors that make it impossible for the larvae of the blue-winged dragonfly to colonize the water include, on the one hand, the canalization and construction of the same, in which the aquatic plants that are important for the settlement are lost. On the other hand, the eutrophication of water bodies by agriculture and household sewage is an important factor in the decline. This leads to increased digested sludge formation and thus increased oxygen consumption in the water bodies concerned, as well as increased algae growth from so-called " slime algae ". These are brown and green algae that overgrow the aquatic plants and the substrate. The algae plants are not accepted by the females as oviposition sites. In addition, the larvae do not find any means of holding against the current, and the algae and dirt particles settle on the gill leaves, which are important for breathing. The algae is followed by weeds and finally silting up of the waters.

However, even near-natural waters with low water pollution can be in a state that is not usable for the animals. The water surface must not be completely overgrown by the plants of the marginal vegetation, this is mainly done by fast-growing plants such as the common meadowsweet ( Filipendula ulmaria ), the great nettle ( Urtica dioica ) or the Indian balsam ( Impatiens glandulifera ). The tree vegetation at the edge of the water may also not show a closed treetop, as otherwise the necessary solar irradiation is missing.

Especially streams in fallow pasture areas, in which no regular mowing takes place, are accordingly not colonizable for the animals. This can be countered by regular removal of the marginal vegetation, which, however, must not be complete. Partial clearing of the trees should also be carried out. In more intensively used agricultural areas with regular input of liquid manure as fertilizer, a few meters wide extensive or uncultivated bank strip can prevent flooding and thus counteract eutrophication.

Systematics

Calopteryx virgo meridionalis

The blue-winged demoiselle represents one of about 20 species of the genus Calopteryx known today. However, it must be noted that a comprehensive systematic genus revision of Calopteryx is long overdue in order to clarify a number of currently controversial points regarding the authorization of individual species or subspecies. In addition to the blue-winged demoiselle there are three other species in Europe, with the bronze demoiselle ( Calopteryx haemorrhoidalis ) and the south-western demoiselle ( Calopteryx xanthostoma ) only occurring in southern Europe. All other species are distributed across the Holarctic and are found accordingly in North America and Asia. The sister species of the blue-winged demoiselle is probably the bronze demoiselle, according to molecular biological studies, the following relationship was found for the European species:

 Calopteryx  

Other Calopteryx species


  European Calopteryx species  
  NN  

Banded demoiselle ( C. splendens )


   

Southwest Demoiselle ( C. xanthostoma )



  NN  

Bronze demoiselle ( C. haemorrhoidalis )


   

Blue-winged demoiselle ( C. virgo )





Within the individual species, various subspecies are discussed, which differ mainly in terms of color. Also hybrids between species should be possible and occur, but were rarely documented.

Individual evidence

  1. Common mermaid (Calopteryx virgo). In: Brehms Thierleben. Ninth volume. Leipzig 1884, p. 516 ( zeno.org ).
  2. dissemination. In: Klaus Sternberg, Rainer Buchwald: Dragonflies in Baden-Württemberg. Volume 1, Eugen Ulmer Verlag, Stuttgart 2000, ISBN 3-8001-3508-6 , p. 203.
  3. B. Misof, CL Anderson, H. Hadrys: A phylogeny of the damselfly genus Calopteryx (Odonata) using mitochondrial 16S rDNA markers. In: Molecular Phylogenetics and Evolution. Volume 15, No. 1, Orlando 2000, pp. 5-14, ISSN  1095-9513 ( .zfmk-molekularlabor.de ( Memento from September 29, 2007 in the Internet Archive ) PDF).

literature

  • Heiko Bellmann: Observe dragonflies - determine. Naturbuch Verlag, Augsburg 1993, ISBN 3-89440-107-9 .
  • Gerhard Jurzitza: The Kosmos dragonfly guide . Franckh-Kosmos Verlag, Stuttgart 2000, ISBN 3-440-08402-7 .
  • Georg Rüppell: Europe's magnificent dragonflies. (= The New Brehm Library ). Westarp Sciences, Hohenwarsleben 2005, ISBN 3-89432-883-5 .
  • Klaus Sternberg, Rainer Buchwald: Dragonflies in Baden-Württemberg. Volume 1, Eugen Ulmer Verlag, Stuttgart 2000, ISBN 3-8001-3508-6 .
  • B. Misof, CL Anderson, H. Hadrys: A phylogeny of the damselfly genus Calopteryx (Odonata) using mitochondrial 16S rDNA markers. In: Molecular Phylogenetics and Evolution. Academic Press, Orlando Fla. Volume 15, No. 1, 2000, pp. 5-14, ISSN  1095-9513 ( zfmk-molekularlabor.de ( Memento from September 29, 2007 in the Internet Archive ) PDF).

Web links

Commons : Blue-winged Demoiselle ( Calopteryx virgo )  - Collection of images, videos and audio files
This version was added to the list of excellent articles on October 27, 2005 .