Palingenia longicauda (Olivier, 1791)
Ephemera longicauda Olivier, 1791: Russev, 1987: 109; Ephemera swammerdiana Latreille, 1805: Russev, 1987: 109.
Order Mayflies (Ephemeroptera)
Family Palingeniid burrowing mayflies (Palingeniidae)
Conservation status: in Bulgaria: Extinct EX.
General distribution. France, the Netherlands, Germany, Poland, Slovakia, Hungary, Serbia, Macedonia, Bulgaria, Romania, the Ukraine.
Distribution and abundance in Bulgaria. It was found in Bulgaria many times in large numbers in the Danube. It is known from 25 localities in the Bulgarian section from Novo Selo to Silistra . It used to occurr in large subpopulations until 1968 . After that it was not found there [2, 3]. Finding of adults near a canal close to Maritsa River near Plovdiv in 1956 and 1958 was also reported .
Habitats. The nymphs are typical inhabitants of the clay substrate in the large European rivers .
Biology. Palingenia longicauda is the largest mayfly in Europe. The nymph is of the "burrowing" type, inhabiting U-shaped holes with a depth of about 25 cm. The mouthparts and the forelegs of the nymph are adapted to burrowing in the clay . The last instar nymphs leave the holes, swim out onto the surface and develop: the females into adults  and the males into subimagines and then into adults. They emerge usually in June, between 4 and 6 p.m. Mating takes place during the half-hour "mass flight", characteristic of this species. Then the males fall into the water, and the fertilized females fly against the current at a speed of about 18 km/h, doing a "compensation flight before egg laying" . The female lays 8 000 – 9 000 eggs that, because of their slow sinking and the speed of the current in the rivers, are driven down many kilometres along the current . Only those eggs develop that fell onto a clay substrate. The larvae hatch in 4-6 weeks and in the course of three years undergo about 20 moultings . They feed on organic matter that they assimilate from the clay consumed [9, 10].
Similar species. Ephoron virgo. It differs by the shape of the elongation of the mandibula, which in Palingenia longicauda is fan-like, with strong chitin teeth, located laterally.
Negative factors. Pollution of the Bulgarian Danube tributaries and of the Danube with industrial waste waters. The extraction of inert materials, destruction and dike building of the banks of the Danube, hydrotechnical constructions .
Conservation measures taken. None.
References. 1. Russev, 1987; 2. Russev & Uzunov, 1991a; 3. Russev & Uzunov, 1991b; 4. Russev, 1966; 5. Russev, 1977; 6. Strenger, 1973; 7. Csongor & Moczar, 1954; 8. Russev, 1959; 9. Unger, 1927; 10. Schoenemund, 1929.
Author: Yanka Vidinova