Once a year in June and July the Tisza river in Hungary, Serbia, and Slovakia for one day is swarmed by thousands of beautiful and rare mayflies. Also known as the long-tailed mayfly, the Tisza mayfly has become iconic in Hungary and their spawning for a few hours every summer attracts tourists from all around.
Taxonomy and Evolution
The Tisza mayfly is the only member of its genus and has the scientific name Palingenia longicauda. As expected from their name, the Tisza mayfly is in fact a mayfly, order Ephemeroptera. The mayflies are some of the earliest orders of insects, and by default animals, to evolve the ability to fly over 300 million years ago. Mayflies have gone strength to strength since then and have evolved into various shapes and sizes. The Tisza mayfly belongs to a very small family of mayflies called Palingeniidae, or ‘spiny-headed burrowing mayflies’, which are also known for their giant size.
Biology and Behaviour
As a mayfly the Tisza mayfly goes through dramatic changes over its life. They start out as tiny eggs on the surface of the water that slowly sinks to the river bed where the larvae inside develop for around 45 days. The nymphs are only a few centimetres at their largest, but they have the two long tails that characterise the adults. Swarms of newly hatched nymphs begin creating u-shaped burrows where they will find safety from predators and somewhere safe to develop for the next three years. Over these years the mayflies will molt to allow themselves to get bigger until they reach their final stage. In their thousands the nymphs will make their way to the water’s surface resting on the surface, plant stems, or rocks where they will molt one last time. From here the nymph loses its gills and even its stomach and blood pumps its way into the newly emerged wings. These mayflies are large reaching lengths of 12 centimetres, 4.7 inches, making them Europe’s largest mayfly.
Now in their adult form the mayflies have two things to do: mate and lay eggs. Using their impressive 6 centimetres wingspan the mayflies fly several between 1 and 3 kilometres over the water’s surface in order to attract mates. Males often skim the surface of the river effectively bumping into females as they finish molting, something which helps as they do not have a lot of time to reproduce. This is done in swarms so the rivers become swamped by thousands upon thousands of mayflies flying around trying to mate with as many other mayflies as they can, with can be done in flight. When inseminated the female, if she can dislodge the male which can be a tricky business due to dangly forelegs, will land on the water’s surface and release her eggs in a trickle. Between 7,000 and 8,000 eggs can be laid by a single mayfly. After that they die. Adult Tisza mayfly only live for a few hours, up to a day max, before they die, hopefully reproducing by then. This normally happens in late June and early July.
Distribution and Habitat
For all of their life Tisza mayflies stick by the water – the only time that they leave the water is to breed before dying. They only can survive in waters with little to no pollution which means they are a good indicator species for the cleanliness of rivers. As a result, they have sadly vanished from most of Europe with them no being limited to the Tisza river (in Hungary, Slovakia, and Serbia), the Ukrina (in Bosnia and Herzegovina), the Prut and the Brega rivers (both in Romania). However, most are found along the Tisza, mostly in the Hungarian and Serbian sectors, where they have become cultural icons. Every June Hungary welcomes the ‘Blooming of the Tisza’ and welcomes the arrival of ‘Tisza flowers’. There are poems and even statues devoted to this event. The nymphs will build tunnels at the bottom of the river where they live together, around 400 can be found in one burrow.
Diet and Predators
As nymphs the mayflies eat algae and plants, as well as any detritous that floats down to the bottom of the river. As adults they do not eat, in fact their digestive system fills with air and their mouth parts shrink to beyond uselessness. Mayflies are food for many different animals. Frogs, toads, birds, dragonfly nymphs, and fish will all eat the mayflies, with the annual blooming also offering a feeding frenzy. However, the sheer number of the mayflies means that the predators will not even put a dent in their numbers. Historically, the mayfly nymphs were popular baits for fishing, but this has been discouraged due to how rare the mayfly now is.
Conservation and Threats
The IUCN has not evaluated the Tisza mayfly but we do know that they are indeed endangered. Once found across Europe they vanished in western Europe by the 1900s and by the 2000s were limited to the above mentioned four rivers, with the overwhelming majority being found in the Hungarian and Serbian section of the Tisza. Pollution decimated their numbers as Tisza mayflies need clean water to survive in and the Hungarian government’s desire to invest in fossil fuels could spell further disaster. However, there have been some positive signs. Genetic testing done in 2012 found that the genetic variability in the mayflies have not been impacted, and Serbia’s recent efforts to reduce pollution has helped the mayflies to spread further in southeast Europe. While the fate of this endagered mayfly still hangs in the balance, it could be a positive sign.
Bibliography:
- William Robinson, Urban Insects and Arachnids: A Handbook of Urban Entomology, (Cambridge: Cambridge University Press, 2005)
- John Brittain and Michel Sartori, ‘Ephemeroptera (Mayflies)’, in Vincent Resh and Ring Carde, (eds.), Enclyclopedia of Insects, Second Edition, (Burlington: Elsevier, 2009), 328-333
- Avar L. Dénes, Romina M. Vaida, Emerencia Szabó, Alexander V. Martynov, Éva Váncsa, Beáta Ujvárosi and L. Keresztes, ‘Cryptic survival and an unexpected recovery of the long-tailed mayfly Palingenia longicauda (Olivier, 1791) (Ephemeroptera: Palingeniidae) in Southeastern Europe’, Journal of Insect Conservation, 26, (2022), 823-838
- Fanni Kaszas, ‘Tisza Mayfly and “Tisza Blooming” becomes Hungaricums as National Values’, Hungary Today, (25/05/2020), [Accessed 11/06/2023]
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