Danube is Blooming Once Again!

Danube witnessed a special event this year, too. After a long break and thanks to the improvement of the quality of the water in the Danube, once again one could witness the wonderful phenomenon of the wedding-dance of the proverbially short-lived mayflies that used to happen only at River Tisza.

It is a special experience to witness the dance of the snow-white insects, which live only a day or two in their fully developed adult form. These species have become very rare and it is especially wonderful news that after several decades they were reborn the second time at the river Danube, since the appearance of these outstandingly environmentally sensitive creatures is also warranty of the cleanness of the water. It seems that international efforts to improve water quality have brought success, because previously for forty years there were no mayflies here, but as surprising as it is, in 2012 the protected “Danube Flowers” reappeared. From the swarming this year, researchers have a reason to hope that these special insects have once again settled down along the Hungarian section of Danube.

Picture: Rácz Gergely

“Danube Flower” (Ephoron virgo), because of its white colour is also called white mayfly. Mayflies are one of the most ancient insects, which had been quite widespread all through Europe, but have been extinct in most of the continent and can be found in large numbers only at River Rába and River Tisza and its affluent rivers in Hungary. That is why it is no coincidence that till now the appearance of mayflies used to be a speciality of River Tisza and it has become a symbol of Hungarian natural values and one of the characteristic icons of River Tisza. Because of this, “Tisza Flowers” (Polingenia longicauda) are much more well-known than their relatives from Danube.

Compared to “Tisza Flowers,” which are 8 to 12 cm, “Danube Flowers” are much smaller, they are maximum half of this size. While Tisza Blooming happens usually twice or three times, Danube Blooming can occur as many as ten-eleven times and that is why it can last till the end of September. Tisza Blooming occurs usually between 6 PM and 8 PM at the beginning of July, while on Danube the wedding dance can be observed between 8.30 PM and 10 PM.

The short life is in fact a characteristic of the fully developed adult insects, in larvae form they can live as long as two or three years. Mayflies lay their eggs on the surface of the water and the eggs later sink to the bottom. In larvae stage they dig themselves deeper and deeper into the sediment; they like oxygen-rich clean water. As larvae they moult 19-27 times and their development can last years. When their spiracles develop, their body fills with air and they rise to the surface. Blooming is those few days when they are mating and their lives come to an end after they lay their eggs.

Picture: Rácz Gergely

Though mayflies in their larvae form avoid light, later they outgrow this characteristic and illuminated bridges, ships and buildings are fatal light-traps for them into which several millions of them fall into. Researchers nowadays work on finding the wavelength and light polarity which would disturb them the least. Due to their protected status, it is prohibited to collect even dead mayflies.