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Budapest mayfly swarms are a result of the low Danube water levels

Due to a hot and unusually dry summer and low water levels, mayflies are more numerous and swarming along the Danube river banks in Budapest this year. They are attracted to the city lights and fill the air.

Mayflies can be in the hundreds of thousands or even millions and they rush to reproduce as quickly as possible before they die. Mayflies only live for a few hours after hatching, and the abundance of these insects is directly related to the health the Danube.

The swarming of Danube Mayflies is usually a phenomenon that occurs in August. This year, however, it started in mid-July and will last for several weeks. Their early appearance as huge swarms may be related to higher temperatures, say researchers.

Gyorgy Kriska is an associate professor at Eotvos Lorand University, Budapest. "We've observed that mayfly swarms are more common in years with low water levels," he said.

In early February, unusually low levels of water on the Danube, Europe’s second longest river, disrupted shipping.

Kriska explained that low water levels encourage the growth of algae, which provides food for mayfly larvae.

The river was so polluted that the mayflies didn't swarm in about 40 years. He said that they returned to the Danube in 2012, when it became cleaner thanks to wastewater treatment plants. Mayflies are a protected species. A single specimen is worth 10,000 forints (30 dollars).

When mayflies are swarming upriver, they can get confused by the city lights and shadows from bridges. This causes them to lay their eggs on the riverbank rather than in the water.

Hungarian researchers installed blue lights to help the pedestrians as much as they could.

Kriska stated that "our lights keep them here... they continue flying in front of lamp... and crash to the water."

This way, we will ensure that the next generation is not drowned and can survive. (Reporting and editing by Giles Elgood, Anita Komuves, Krisztina Feenyo)

(source: Reuters)