Uferaas
| Uferaas | ||||||||||||
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Shore Aas ( Ephoron virgo ) |
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| Systematics | ||||||||||||
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| Scientific name | ||||||||||||
| Ephoron virgo | ||||||||||||
| ( Olivier , 1791) |
The shore eagle ( Ephoron virgo ), also known as the ephemeral maiden , is a species of the mayflies belonging to the insect group and is widespread in the Palearctic . The species is known for its mass swarms on August or September evenings, when the animals are also strongly attracted by light. The name Uferaas is sometimes used for other species of mayflies, such as B. Palingenia longicauda or other species of the genus Palingenia .
characteristics
The body length is 10–18 mm, the tail threads (2 cerci in the male, 2 cerci + 1 terminal filum / paracercus in the female) measure a further 15–35 mm. The fore wing length is 10-16 mm. The complex eyes are black, the antennae are white. The prothorax is white, the mesothorax light brown. The species can be recognized by its milky white wings, which are transparent in the males and opaque in the females. The front legs are basally black and distally white, the middle and rear legs are white. The front legs of the males are longer than body length, those of the females are very short. The cerci and paracercus are colored white, the paracercus of the male is only rudimentary.
The eggs measure around 260 × 175 µm and have a clear polar cap that immediately shows individual thick threads after contact with water.
The larvae are 12-20 mm long, yellowish-white in color and have 7 pairs of gills on the abdomen, the first of which is leaf-shaped and the other two-branched with fringes.
The Subimago is similar to the Imago , but the wings are gray-white in color and the females are darker than the males and have a reddish-yellow abdomen. The females always remain a subimago and do not molt to the imago.
distribution and habitat
The species lives in large parts of the Palearctic region, from North Africa and Western Europe to East Asia. She is known z. B. from Spain (e.g. in the Ebro ), France , Switzerland , Belgium , the Netherlands , Germany , Hungary or Estonia .
The larvae live in the potamal of medium and large rivers.
way of life
The larvae hatch from the eggs in spring from the end of April and develop over a period of three to four months. They live on and in the river sediment. The first stages have no tracheal gills and live freely in the substrate, for example in the gap system of grains of sand. Later they dig horizontally U-shaped tubes into the river sediment. Here, with their feathery tracheal gills , they create undulating movements, causing a stream of water to flow through the tube, providing oxygen and food such as detritus and algae , which are filtered out of the water. The finest food particles up to 1 µm in size are filtered out with the mouth parts.
When the larvae reach the subimago stage in August or September, they swim to the surface of the water where they emerge. Shortly after dusk there are mass swarms over the rivers. The males appear earlier than the females and land on the bank of the river, where they molt to the imago. After that, they return to the river to fly horizontally above the surface of the water looking for emerging females. The females remain subimagos throughout their adult lives and are fertilized in flight. The flight time lasts about an hour, then the adults die . The females fall on the surface of the water, their abdomen bursts open and after touching the surface of the water they release two egg packets with a total of 2000–3000 eggs. The egg packets fall apart in the water and the eggs sink one by one to the bottom of the river, where they are attached to the ground with the sticky polar cap so that they do not drift further downstream with the water current. In winter the eggs are in a diapause, which is deactivated in spring by rising temperatures.
The species is strongly attracted by light, so the adults often buzz around street lamps near the water, where they eventually die without being able to lay their eggs in the water. As a protective measure, light sources are sometimes placed on bridges over the rivers. Here the mayflies often fall prey to fish or other predators, but are not lured away from the waters.
Danger
Ephoron virgo was considered to be extinct or lost in Germany in the early 1980s, but was found again in the Rhine and Danube in the 1980s . After this time, the increasingly better water quality of the rivers also spread to the Altmühl , Fulda , Main , Mosel , Naab , Weser , Isar , Regen and Regnitz . On the Naab in the Upper Palatinate district of Schwandorf (places Nabburg , Schwandorf and Schwarzenfeld ), mass synchronous slip events still occur today.
In Saxony around 1900 the adults from Ephoron virgo on the Upper Elbe were hatched in so large numbers that this event was referred to as a “snowstorm in summer”. The residents in the villages on the Elbe in Saxon Switzerland and Bohemia rushed over in the evening and lured the animals with fire, causing their wings to burn and perish. The bodies were dried and sold as food for songbirds. The last evidence of this species from Saxony dates back to before the Second World War. The species became extinct in Saxony. The species is also extinct in Switzerland, where the only evidence comes from 1870. In Bavaria, a stabilization or an increase in stocks can be assumed due to the improved water quality in the lower reaches of the Naab and Regen. In Cologne on the Rhine, mass swarms could also be observed on August evenings from 1990 to 1992.
Taxonomy
The species was first described in 1791 by Guillaume-Antoine Olivier under the name Ephemera virgo . Another synonym is Polymitarcys virgo ( Olivier , 1791), which can also be found in the spelling Polymitarcis virgo .
literature
- Michael Chinery : Parey's Book of Insects . Franckh-Kosmos Verlags-GmbH & Co., Stuttgart 2004, ISBN 3-440-09969-5 , p. 18.
- Jiří Zahradník: The Cosmos Insect Guide 6th edition. Franckh-Kosmos Verlags-GmbH & Co., Stuttgart 2002, ISBN 3-440-09388-3 , p. 90.
Web links
- Matthias Nuss: Ephemeral Virgin ( Ephoron virgo (Olivier, 1792)). In: insekten-sachsen.de. Retrieved August 1, 2021 .
Individual evidence
- ↑ Núria Cida, Carles Ibáñez & Narcís Prat (2008) Life history and production of the burrowing mayfly Ephoron virgo (Olivier, 1791) (Ephemeroptera: Polymitarcyidae) in the lower Ebro river: a comparison after 18 years. Aquatic Insects 30 (3): 163-178. doi: 10.1080 / 01650420802010356 . Link to the PDF .
- ↑ a b Ephoron virgo at rheinstation.uni-koeln.de, accessed on August 1, 2021.
- ↑ Federal Office for the Environment FOEN, Swiss Center for the Cartography of Fauna (SZKF / CSCF), Neuchâtel (2012) Red Lists of Mayflies, Stoneflies, Caddis Flies - Endangered Species in Switzerland, as of 2010.
- ^ Red list of endangered mayflies (Ephemeroptera) of Bavaria, edited by Georg Adam 2003. Link
- ↑ Ephoron virgo (Olivier, 1791) in GBIF Secretariat (2021). GBIF backbone taxonomy. Checklist dataset [1] accessed via GBIF.org on August 1, 2021.