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Europe's largest mayfly
Nothing this large on the Teifi....
These mayflies which can grow up to 12cm in body length, 25cm including the tail, live in the slow moving River Tisza, a tributary of the Danube that flows through Ukraine, Romania, Hungary and finally Serbia where it meets the Danube.
Nymphs live in the muddy river banks in a U shaped burrow for three years and hatch in their millions over a short period which lasts for just three or four days, usually in late spring. Hatches are on such a breathtakingly large scale that they have become famous and generate nature tourism to the famous areas of river. Despite their localised abundance the species is on the decline and are now extinct in some of the Polish rivers they formerly thrived in.
The nymphs (above) are a popular bait, in the past they were dug out from the river banks by fishermen but now they're a protected species and their use is banned. Unfortunately ( almost inevitably ) the real threat comes from polluting chemicals, the water quality of the Tisza is declining and has recently been polluted on a huge scale -
"In February 2000, tons of dead fish bobbed aimlessly down the Danube and Tisza rivers in Europe. Birds and other wildlife were also found dead and nearby towns were forced to close their water intake systems. The toxic bullet had been a cyanide spill from a gold mine in Baia Mare, northern Romania. To this day, it has left a legacy of dead rivers and polluted lands and stands as a cruel testament to the dangers of using a lethal chemical in mining."
Despite these threats the mayfly remain and have has found a place in the hearts of the people from around the river where the Hungarians in particular have a soft spot for them. The hatch is known as "The Blooming of the Tisza" due to the number of mayflies covering the surface of the river creating an impression of a flower meadow, the mayflies are known colloquially as "Tisza Flowers".
One of the interesting behavioral aspects of these mayfly is related to the slow moving rivers which they inhabit. Males skim over the surface film of the river rather than fly above it in the way that most mayfly do. This would be suicidal in an environment which held surface feeding fish, a trout stream for example, but in an environment which mainly contains fish that feed at lower depths the behaviour has a distinct advantage. Females can be targeted as they struggle to break free from the water rather than captured or captivated in flight- basically it cuts out a lot of wasted effort usually invested in courtship displays.
Once the eggs are deposited in the water surface they drift down to the silt of the river bed. After forty five days the eggs hatch and the larvae which gather to form dense colonies begin to dig their tunnels and the cycle is repeated in the following years.