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The order Megaloptera, formerly considered a suborder (Sialodea) of Neuroptera, is generally considered to be among the most primitive of the holometabolous insect orders. It contains two families, the Sialidae (alderflies) and the Corydalidae, the latter subdivided into the Corydalinae (dobsonflies) and the Chauliodinae (fishflies). The fauna of Megaloptera consists of about 300 extant species worldwide (New and Theischinger 1993). A list of all megalopteran genera is available here.
A typical dobsonfly male with elongated mandibles. Corydalus imperiosus Contreras-Ramos (Corydalidae: Corydalinae), Misiones, Argentina. Photograph copyright © 1997, Atilano Contreras-Ramos
Like Ephemeroptera, Odonata, Plecoptera, and Trichoptera, the order Megaloptera is entirely aquatic, i.e., all--or nearly all--megalopteran species have at least one aquatic stage. Adults of Corydalidae are particularly noteworthy for their frequently large size, and, in many species of the genera Corydalus and Acanthacorydalis, for the extremely elongated mandibles of adult males. Adult fishflies and dobsonflies are generally nocturnal and secretive, while alderflies are diurnal yet not too frequently collected. At the right place and time of the year (e.g., near the edge of clean lakes in Minnesota, U.S.A., around June), however, it is possible to find individuals of the fishfly Chauliodes rastricornis Rambur congregating under lights, or aggregates of alderflies on vegetation during day time.