Western wedge maiden
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Western wedge damsel ( Gomphus pulchellus ), male |
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| Gomphus pulchellus | ||||||||||||
| Sélys , 1840 |
The western wedge damsel ( Gomphus pulchellus ) is a species of dragonfly from the family of the river damsel (Gomphidae). This yellow-black colored dragonfly (Anisoptera) is the only member of its family that predominantly inhabits stagnant water - all other gomphids need flowing water for their larval development. In Central Europe it was considered extremely rare until a few decades ago; The species is now showing a tendency to spread and can be encountered more frequently in river valleys with gravel quarries. The scientific name, made up of Greek and Latin, means something like "pretty wedge".
features
The species is a relatively slender and gracefully built wedge maiden; it reaches a body length of 45 to 50 millimeters and a wingspan of 60 to 70 millimeters. The legs are striped black and yellow. To distinguish it from other Gomphus species, the exact arrangement of the black stripes on the yellow chest ( thorax ) is important (see photos). The black lines there are quite narrow, which also applies to the dark drawing elements of the body as a whole. As a result, the animals appear relatively bright , similar to the Asiatic maidenhead ( Gomphus flavipes ). At least juvenile specimens are bright yellow, which, however, fades with age and turns into a gray olive.
The rear abdomen is not clubbed in either the males or the females. While in the males the second segment of the abdomen is constricted like a waist, the females have a uniformly thick cylindrical abdomen. There is a possibility of confusion with various other maidenheads, including Gomphus flavipes and Gomphus simillimus (other species in southern Europe).
The larvae and, accordingly, the exuvia that can later be found on land, are built similarly flat as those of the common wedge damsel ( Gomphus vulgatissimus ), but have a longer abdominal tip at the back, which is not as elongated as in the Asian wedge damsel.
distribution and habitat
The main range of the species is in southwest Europe, namely on the Iberian Peninsula and in France; later Switzerland was added. Austria counts as the most easterly secured individual record, whereas finds from Romania, Bulgaria and Slovakia are in doubt. At the beginning of the 20th century, the Rhine was still considered the north-eastern boundary of the species; Germany is therefore not considered to be populated by Gomphus pulchellus . In the meantime, however, the distribution area has again expanded significantly to the northeast; There are now observations from northern Lower Saxony ( East Frisia , Elbe-Weser triangle ) and Saxony-Anhalt. It spreads towards the east via the Danube and Main . The Upper Rhine Plain is currently named as the main occurrence in Germany.
The expansion of the distribution area is explained on the one hand by climatic changes and on the other hand by an increased biotope offer. The Western Keiljungfer mainly uses quarry ponds in gravel pits as secondary habitats and has thus benefited from their increase. Large-scale wet excavation sites for gravel and sand often arise in floodplains in particular. Today these clear quarry ponds with little vegetation represent the most important habitat type of Gomphus pulchellus ; In addition, it populates reservoirs, eutrophic moor ponds, oxbow lakes of rivers, river underflows and wide, sluggishly flowing canals. Common features of these waters are sunny, open (sparsely overgrown) sand, gravel or scree banks, connected with deeper water zones that have fine-grained to muddy sediments.
The common wedge maiden sometimes occurs syntopically at larger lakes. Other dragonflies that are often associated with the western wedge maiden are the great blue arrow , the common mug maiden and the great pitch dragonfly .
Way of life
Larvae
The larvae of the western wedge damsel live in the bottom of the water, for example in sediments of coarse detritus , between submerged fallen leaves or in the crevices between rocks. Younger stages seem to prefer the finer sandy subsoil, older ones tend to prefer coarse sand and gravel. A flow through the body of water is not necessary, but is at least tolerated. Thanks to their mostly nocturnal and underground activity, the larvae can also survive in lakes with high predation pressure from fish and build up populations with strong abundance . They hunt in the sediment of all kinds of small animals such as sludge tube worms , midge larvae , roll-leeches and mud fly larvae. They usually have a two-year, sometimes three-year development time in which they go through up to 15 molting stages.
Adults
The emergence, i.e. the hatching of the adults , begins in Central Europe from the beginning of May. The flight time lasts until August, with the focus being in June and July. The lifespan of an adult dragonfly of this species is estimated at a maximum of about 45 days.
The hatch sometimes takes place just a few centimeters from the waterline on structures of all kinds (plants, driftwood, stones, etc.). Sometimes the abdomen is even submerged. Other larvae also move several meters away from the water or climb up to two meters into the bank structures. The hatching process takes place within a quarter of an hour to an hour and is therefore of very short duration for a dragonfly. In spite of this, and also in the subsequent hardening phase, a large number of individuals fall victim to waves or predators such as white wagtails , sparrows , frogs or ants .
After hatching, the young adults leave the water area and during a maturation period of several weeks spread over a radius of several hundred meters, sometimes even a few kilometers in the surrounding area. Here they hunt for insects on sunny meadows, forest aisles or in tall herbaceous meadows. They prefer seated or low-flying prey that they press to the ground under their thorax, such as cabbage snakes ( Tipula oleracea ). As sexually mature animals, they return to the water. Here the males prefer to stay on sunny sand and gravel banks close to the water and are not very happy to fly. They are relatively peaceful with one another; on the other hand, attacks are more frequent compared to simultaneously active Great Blue Arrows.
If a female flies to the water, this is usually taken immediately by a male. The actual pairing wheel is always formed above the water at a height of two to four meters; the copulation is then continued in the bank vegetation.
When laying eggs, the female squeezes out an egg ball while sitting, which is then wiped off in portions on the surface of the water by briefly dipping the abdomen repeatedly. The eggs sink to the bottom of the water and stick to the sediment with the help of a sticky gelatinous disk.
Hazard and protection
According to the German Federal Nature Conservation Act and the Federal Species Protection Ordinance, the Western Keiljungfer is a "specially protected" species. Its original primary biotopes - floodplains with natural process dynamics - are barely available in Central Europe or have been completely anthropogenic . Therefore, the species is now heavily dependent on replacement habitats such as quarry ponds. There, eutrophication , stocking with deeply rooting fish ( carp etc.) as well as intensive leisure activities by anglers and bathers can impair the survival of the larvae in the water bed.
literature
- Heiko Bellmann: The Kosmos dragonfly guide. Franckh-Kosmos Verlags GmbH & Co., Stuttgart 2007, ISBN 978-3-440-10616-7 .
- Klaus Sternberg, Bernd Höppner, Adolf Heitz, Stefan Heitz: Gomphus pulchellus Sélys, 1840 - Western wedge maid. In: Sternberg, Buchwald (ed.): Die Libellen Baden-Württemberg. Volume 2: Dragonflies (Anisoptera). Ulmer, Stuttgart 2000, ISBN 3-8001-3514-0 , pp. 293-303.
Web links
- More pictures and information at www.natur-lexikon.com (Attention: Website not ad-free!)
- Gomphus pulchellus inthe IUCN 2013 Red List of Threatened Species . Posted by: Boudot, J.-P., 2009. Retrieved February 18, 2014.
Individual evidence
- ↑ Entry on Gomphus pulchellus at wisia.de