Order Megaloptera

Themes > Science > Class Insecta > Insect Orders > The Endopterygota > Order Megaloptera

Introduction

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.

Characteristics

Adults of Megaloptera can be identified by the enlarged and fan-folded anal area of their hind wings (Borror et al. 1989). Those of Corydalidae are large (forewing longer than 15 mm, wingspan up to 180 mm), pale yellowish to brownish or spotted black, with ocelli, and their 4th tarsal segment is simple; while those of Sialidae are small (forewing 15 mm or less), dark brown to gray and black (sometimes with orange spots on the head), lack ocelli, and their 4th tarsal segment is bilobed.

Larvae are elongate, moderately flattened, prognathous, have a distinct labrum, and measure 10-90 mm when mature. Mouth parts are of the chewing type, well developed. Larvae bear lateral abdominal filaments (on segments 1-8 in Corydalidae, and 1-7 in Sialidae) and either a pair of anal prolegs (Corydalidae) or a single caudal filament (Sialidae). Members of the subfamily Corydalinae also possess tufts of accesory tracheal gills under the lateral filaments of segments 1-7 (Evans and Neunzig 1996, Theischinger 1991).