Harris' Mayfly
Brachycercus harrisella Curtis, 1834
Order Mayflies (Ephemeroptera)
Family Small square-gilled mayflies (Caenidae)
Conservation status: in Bulgaria: Critically endangered CR [A2a; B1ab(iv); D; E].
General distribution. Great Britain, the Scandinavian Peninsula, Denmark, Germany, Poland, Spain, France, Northern Italy, Hungary, the Balkan Peninsula, European Russia.
Distribution and abundance in Bulgaria. Found in the Danube near Kozloduy and in the Maritsa River near Dimitrovgrad and Harmanli between 1955 and 1964 in few spewcimens [1, 2]. It has not been recorded during investigations since 1973 in the Maritsa River [3, unpublished data] and in the Bulgarian Danube section [4].
Habitats. A typical inhabitant of psammorheophilic biocenose of large, slow-flowing continental rivers [1, 5] but it also occurs in smaller rivers and streams in foothills, as well as in marshes and especially in muddy sections near the shores [6].
Biology. One generation per year. The species overwinters in the egg stage and after its hatching the nymph develops very rapidly (in the course of 2-3 months) [7, 8]. Adults fly at the end of July and throughout August [9], usually late in the evening or during the night. They live in the course of 4 to 10 hours [10]. The nymphs are of the crawling type. They are mainly detritophagous and feed on finely suspended organic matter [6]. An adaptation for inhabiting hard muddy deposits is the presence of a swelling at one end of the dome-like ventral side of the body, with the help of which the nymph digs a furrow in the substrate. The lateral processes of the abdominal segments also contribute for this [8].
Similar species. Cercobrachys minutus, from which it differs with the presence of three cone-like spikes of the head of the nymph.
Negative factors. Pollution of the large lowland rivers with domestic and industrial waste waters. Hydrotechnical construction. Extraction of inert materials from the bottoms of rivers.
Conservation measures taken. None.
Conservation measures needed. Prevention of the pollution of the middle and lower courses of the larger rivers. Restoration of the habitats of the species in which it occurred in the past.
References. 1. Russev, 1959; 2. Russev, 1966; 3. Uzunov et al., 1981; 4. Russev, Uzunov, 1991a; 5. Brittain, 1972; 6. Elliott et al., 1988; 7. Sowa, 1975; 8. Landa, 1968; 9. Elliott, Humpesch, 1983; 10. Soldan, 1986.
Author: Yanka Vidinova
