During the JDS2 on the upper Danube River, on the stretch between Regensburg and Deggendorf in Germany, we observed a very impressive event that occurs only a few days a year in August - the mass emergence of the mayfly Ephoron virgo.
Bridges and ships were covered by millions of these insects which were attracted by artificial lighting. Standing near the lanterns was like being in a snow shower. The main flight activity, recorded from August 12 to 16, started daily at 9:30 p.m. and ended at about midnight.
The phenomenon of this mass emergence was already observed about a hundred years ago, but it disappeared for many years due to water pollution in the 20th century. It is a moot question whether the species was totally lost during this period because of the difficulties of sampling its larvae in large rivers and accordingly, the insufficient data available. However, in the late 1980s and 1990s, its mass flight activity recurrence was observed which can be contingently ascribed to less pollution of the Danube.
Air-lift sampling, as done on the JDS2, now makes sampling possible at any location in large rivers. As a result, JDS2 sediment sample findings also included the larvae of Ephoron virgo located in the stretch between Regensburg and Deggendorf.
