The order Megaloptera belongs together with Raphidioptera and Neuroptera to the superorder Neuropteroidea. Megaloptera is a species-poor insect group, consisting of about 300 species worldwide (New and Theischinger, 1993 in Contreras-Ramos, 1997).
The order includes two families: Corydalidae with the subfamilies Corydalinae and Chauliodinae and Sialidae. Only the family Sialidae has representatives in Europe (Contreras-Ramos, 1997).
The Bulgarian alderfly fauna comprises only 3 species (of a total number of 6 European species), all of them belonging to the genus Sialis (fam. Sialidae) (Popov, 1981):
Sialidae
Sialis lutaria
Sialis fuliginosa
Sialis nigripes
