Pitch dragonflies

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Pitch dragonflies
Great pitch dragonfly (Ischnura elegans), young male

Great pitch dragonfly ( Ischnura elegans ), young male

Systematics
Order : Dragonflies (Odonata)
Subordination : Dragonfly (Zygoptera)
Superfamily : Coenagrionoidea
Family : Dragonfly (Coenagrionidae)
Subfamily : Ischnurinae
Genre : Pitch dragonflies
Scientific name
Ischnura
Charpentier , 1840

The pitch dragonflies ( Ischnura ) are a worldwide common genus of the slender dragonflies (Coenagrionidae) within the small dragonflies (Zygoptera). They are known for the different, sometimes strongly colored variants that females in particular can adopt. In Central Europe there are two species of the genus, the large and small pitch dragonfly ( Ischnura elegans and Ischnura pumilio ). In southern Europe and North Africa, the great pitch dragonfly is being replaced by very similar species.

features

Ischnura elegans f. rufescens ; In this female color variant of the great pitch dragonfly, no lateral humeral stripe is formed.
With the females, here Ischnura senegalensis , strong colors are typical in the youthful dress.
This male of Ischnura aurora also has the typical blue “bottom light”, but the abdomen is not drawn dark.
The females of the lesser pitch dragonfly ( Ischnura pumilio ) are not at the bottom.
Androchrome female of the Australian Ischnura heterosticta

Pitch dragonflies are typical, mostly relatively small, slender dragonflies with a body length between twenty and forty millimeters and an elongated abdomen , which is typically metallic black on the upper side . One or more of the posterior abdominal segments are often brightly colored, usually blue, and thus form a conspicuous “tail light” that contrasts with the basic black color. However, there are also species in which the black color of the abdomen is not complete, as well as those that do not bring up the rear. The black coloration, which causes the dark impression characteristic of the pitch dragonflies when viewed from above, is only on the upper side of the abdomen; the middle segments on the sides and below are light, mostly yellowish, so that the pitch dragonflies are not particularly dark in color when viewed from the side appear.

Most species have bright, clearly formed postocular spots on the body-facing side of the compound eyes . These vary greatly in size and shape between the species, often with the females - more rarely with the males - they are connected by a light line. The eyes are dark on top, so that they appear to be covered by a cap. In addition, there are sometimes colored, horizontal stripes in the middle of the eyes, these are usually missing in fully mature individuals. In the middle of the upper side of the thorax there is always a dark median stripe, usually - except for some female color variants - the lateral, dark humeral stripes are also formed. The light ante-humeral stripes in between do not have to be present, or in some males they may be resolved to points that are apart. The side stripes of the thorax are only weakly developed or are completely absent - especially again in some female color variants - so that the sides of the thorax appear light and without drawing.

As with all slender dragonflies, the wings are stalked on the body. Fore and hind wings are the same and always hyaline . A distinguishing feature from other slender dragonflies is the rhombic, two-colored pterostigma in most species , which is usually black at the base of the wing and white on the wing tip. The wing marks also differ in size and shape between the front and rear wings.

The females of the pitch dragonflies are known to come in different colors. Androchromic females are colored like males, but more often heterochromic (female-colored) colourations are formed, these sometimes with several color variants, which in turn change significantly with the onset of sexual maturity. A bright orange or pink color is typical of the juvenile form, in some species this covers the whole body. With the maturation of mature Imago , the colors darken increasingly. In addition, the sexually mature pitch dragonflies of some species form a mostly bluish or whitish wax ring, which can cover the markings on the body. There is a protruding spike in front of the ovary on the eighth abdominal segment. Like the development of polychrome forms, this is a characteristic of the Ischnurinae .

A green thorax with a dark abdomen and blue tail light is typical of the male pitch dragonflies, but there are also other color variants. In supervision, the end of the abdomen with the cerci appears to be forked in most species, which earned them the name “forktails” in America and Canada. The coloring of the males also differs considerably between the youth and age forms.

Similar species

Due to the typically black abdomen with the noticeable tail light, it is usually relatively easy to differentiate the pitch dragonflies from other slim dragonflies such as the azure and goblet maiden . These form species-specific drawings of the abdominal segments that taper from the side, taper cranially and thus do not completely cover the upper side of the abdomen. The drawing of the abdomen is mostly opaque on the upper side of the pitch dragonflies and the sides are parallel. Some representatives of the azure and goblet maiden, however, also show patterns and taillights, as they are typical for the pitch dragonflies, for example the Northern European crested azure maiden ( Coenagrion armatum ) with also green thorax and blackened abdomen.

distribution

The pitch dragonflies are found all over the world, including on many oceanic islands. In Central Europe, the genus is represented by the small pitch dragonfly ( Ischnura pumilio ) and the large pitch dragonfly ( Ischnura elegans ), the latter being replaced by very similar species from the species complex of the Elegans group in the western Mediterranean and North Africa . Their representatives show slight differences in the design of the color variants, but are otherwise so similar that a distinction can only be made on the basis of the male abdominal appendages and the shape of the prothorax or the different areas of distribution. Ischnura graellsii is found in parts of Spain and North Africa, Ischnura genei on the Mediterranean islands and Ischnura saharensis in North Africa . Here there is also an overlap of species of the Elegans group with Ischnura fountainei .

The isolated population of the parthenogenetically reproducing enigmatic pitch dragonfly ( Ischnura hastata ) on the Azores is a specialty .

In North America, 14 species of the genus can be found, some with pairs or trios of species that occur at the same time in the same habitat and cannot be distinguished from one another without closer examination of the male abdominal appendages. However, the males of five of the American species are very different from other pitch and slender dragonflies.

Pitch dragonflies prefer to stay in the dense vegetation around their developing waters, some species also fly over the open water. Preferred habitats are ponds, lakes and bog waters, in which the dragonflies can sometimes reach very high population densities. However, there are also species that prefer streams and rivers. Although many species have a large range, pitch dragonflies are relatively poor fliers.

Way of life

The pitch dragonflies are univoltin in Central Europe , which means that they only develop one generation per year. In the warmer southern Europe as well as in the south of North America, on the other hand, several generations can be trained. The size of the adults is correlated with the time of hatching - larger individuals, whose larval development time was prolonged by the winter months, are mainly found in spring, while smaller individuals can be observed in summer and autumn. In general, the pitch dragonflies have a longer flight time compared to other slender dragonflies and tend to remain in the developing water during the maturation period. For reproduction, the pitch dragonflies come together in the mating wheel, the length of the mating varies greatly between species. The subsequent oviposition, usually in parts of the plant protruding from the water, is only carried out by the female, without the male attached and typically in the early morning hours - often only once.

Naming

In this female from Ischnura cervula , as with the European representatives, the eponymous dorsal black color dominates.

The German name Pechlibellen is derived from the predominantly black abdomen of the Central European representatives, which therefore appear very dark or pitch black . The term "Ischnura", chosen by Toussaint von Charpentier as a scientific generic name, is formed from ischnos ( Greek ) for thin, slender and ura (Greek) for tail or abdomen, even if the pitch dragonflies are not a particularly slim abdomen compared to other slender dragonflies have.

species

The genus of pitch dragonflies was created by Toussaint von Charpentier in 1840 , the type species is the great pitch dragonfly . According to Schorr et al. In 2013 the following 70 species are classified as pitch dragonflies:

swell

literature

  • John C. Abbott: Damselflies of Texas: a field guide. University of Texas Press, Austin 2011, ISBN 978-0-292-71449-6 .
  • Klaas-Douwe B. Dijkstra: Field Guide to the Dragonflies of Britain and Europe. British Wildlife Publishing, Gillingham 2006, ISBN 0-9531399-4-8 .
  • Dennis Paulson: Dragonflies and Damselflies of the East, Princeton Field Guides. Princeton University Press, New Jersey 2011, ISBN 978-0-691-12283-0 .
  • Dennis Paulson: Dragonflies and Damselflies of the West, Princeton Field Guides. Princeton University Press, New Jersey 2000, ISBN 0-691-12281-4 .
  • Jill Silsby: Dragonflies of the World. Smithsonian, Washington 2001, ISBN 1-56098-959-9 .
  • Klaus Sternberg, Rainer Buchwald (ed.): The dragonflies of Baden-Württemberg. Volume 1: General part, dragonflies (Zygoptera). Verlag Eugen Ulmer, Stuttgart 1999, ISBN 3-8001-3508-6 .

Individual evidence

  1. ↑ a b c d e f John C. Abbott: Forktails, Genus Ischnura. In: Damselflies of Texas. Pp. 106-107.
  2. ↑ a b c d e Dennis Paulson: Forktails Ischnura. In: Dragonflies and Damselflies of the East. P. 127.
  3. ↑ Klaus Sternberg: Ischnura elegans. In: The dragonflies of Baden-Württemberg. P. 335.
  4. ^ Jill Silsby: Subfamily Ischnurinae (Blue-tailed Damselflies). In: Dragonflies of the World. Smithsonian, Washington 2001, ISBN 1-56098-959-9 , pp. 110-112.
  5. ^ A b Reinhard Jödicke: Ischnura Chapentier, 1840. In: Dijkstra: Field Guide to the Dragonflies of Britain and Europe. Pp. 90-91.
  6. ↑ Dennis Paulson: Forktails Ischnura. In: Dragonflies and Damselflies of the West. P. 107.
  7. ^ Heinrich Fliedner: The scientific names of dragonflies in Burmeister 's 'Manual of Entomology' . In Virgo, bulletin of the Mecklenburg Entomological Association 9/2006 ( Download ; PDF; 227 kB).
  8. ^ Martin Schorr, Dennis Paulson: World Odonata List. Update from February 5, 2013 ( download ).

Web links

Commons : Ischnura  - collection of images, videos and audio files