Palingenia longicauda is an aquatic insect in the order Ephemeroptera.

[1][2] Unlike many other species of mayflies, adult P. longicauda never move away from water; they fly low and their cerci are frequently touching or sweeping the surface.

Now extinct in many European countries, it can be found on the Tisza river (in Slovakia, Serbia and Hungary),[1] on the Prut and Bega (in Romania)[4] and on Ukrina (in Bosnia and Herzegovina).

Large numbers of P. longicauda larvae will usually hatch and mature during a week in mid June; this natural phenomenon is known as the 'blooming of the Tisza' or 'Tisza blooming' and is a tourist attraction.

Females will fly 1–3 km before laying their eggs on the river, which then sink to the bottom and hatch after about 45 days.