Discuss as:

River seems to bloom as millions of mayflies hatch

Laszlo Balogh / Reuters

A boy swims with long-tailed mayflies (Palingenia longicauda) in the Tisza River near Tiszainoka, 84 miles southeast of Budapest, June 23.

By Katie Cannon, NBC News

From late spring to early summer every year, millions of short-lived, long-tailed mayflies engage in a frantic rush to mate and reproduce before they perish in just a few hours after hatching during "Tiszaviragzas," or Tisza blooming season. After mating, females lay their eggs that sink to the bottom of the river where larvae emerge about six weeks later. The larvae, or nymphs, mature in the mud for three years before they hatch and begin the cycle again.

Tisza mayflies are the largest mayflies in Europe and can grow up to 5 inches long. While they were once found in a number of European countries, they can now only be observed in the River Tisza, a tributary of the Danube that winds through Serbia, Hungary and Romania. 

Laszlo Balogh / Reuters

A man holds a long-tailed mayflies.