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Schopfheim (dpa) - A little somersault here, a pirouette there - and a constant swirl of the filigree legs: There's a lot going on in this water glass.
Rare "fairy shrimp" cavort in it, a species of tadpole shrimp that is estimated to be 400 million years old.
Hartmut Heise, 76 years old and nature conservation warden, has just fished them out of the Eichener See in southern Baden - with special permission from the authorities, because the approximately two centimeter tall animals are strictly protected.
When he talks about the crabs, Heise goes into raptures: “They glide wonderfully through the water, fairy-like, hence the name,” he says.
That animals can live in this lake is quite remarkable.
Because most of the time the body of water doesn't even exist.
It is a temporary lake that only comes to light when it rains a lot in the area or when thawing water occurs due to melting snow, as Heise explains.
Because of an impermeable layer at a depth of 48 meters, the water cannot flow well downwards.
Run over this "tub", the lake appears.
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For years it was not as big as it is now, says Heise: about 270 meters long and 150 meters wide.
After a certain time, the lake "crumbles back into its subterranean labyrinth" of caves in the limestone landscape.
So how do animals manage to colonize this capricious body of water?
With a special strategy, explains Hans Pellmann, biologist and head of the Museum of Natural History in Magdeburg.
In his museum he looks after a collection of all tadpole shrimp species that occur in Germany from various sites.
The females of the “Tanymastix stagnalis” - that's the scientific name of the oak fairy shrimp - lay eggs in the water, in the shell of which they develop into so-called cysts, explains Pellmann: an extremely resistant permanent form.
These cysts withstand the drying up of the lake without any problems, then persevere on the sward and even survive a farmer coming once a year and mowing the meadow.
"The permanent form allows the animals to colonize such extreme biotopes that are only rarely and then only briefly filled with water," says Pellmann.
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If the lake fills up again - even if it does not happen for several years - fairy crab larvae hatched within a few days.
After three to four weeks, the animals are fully grown and can mate.
During their short life, the back swimmers are constantly on the move, says the biologist.
With their eleven pairs of legs, they swirled plankton into the belly groove, from where the food reaches the mouth.
There the food is then chopped up and pressed into the digestive tract, explains Pellmann.
According to the museum director, there are a total of eleven known species of tadpole shrimp in Germany - two of which, however, are probably already extinct.
By the way, primeval cancer is not a technical term, he emphasizes.
The oak fairy shrimp can only be found in a handful of other places except in southern Baden, including in a Bavarian body of water and in a small area on the edge of the Elbe in Brandenburg.
The Krebschen also seem to enjoy a special affection at Pellmann: "They look really nice," he says.
At Eichener See, nature conservation warden Hartmut Heise finally releases his protégés into freedom.
Because of her, the water is currently a true place of pilgrimage, says the 76-year-old.
On the weekend masses of onlookers flocked, and in the past few days he has accompanied several television teams to the shore.
The magic should last for another three to four weeks.
Then the lake will be gone again, says Heise.
Who knows when it will appear again - and with it the back swimming tadpole shrimp.
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© dpa-infocom, dpa: 210312-99-789944 / 2
Information about the "Eichener Feenkrebs" of the AG Tadpole Shrimp from Magdeburg