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Megaloptera (alderflies; class Insecta, subclass Pterygota) Order of mandibulate endopterygotes, which have two dissimilar pairs of wings and whose larvae are aquatic. The larvae have well-developed mandibulate mouth-parts, functional legs, and lateral, abdominal gills. The pupae are adecticous and exarate, pupation taking place in a silken cocoon spun from the larval anus. The predacious larvae are an important part of the diet of freshwater fish, and are often used for bait. Many adults are large, Corydalus (American Dobson fly) having a wingspan of 16 cm. This small order comprises some 300 described species, most of which occur throughout the temperate regions, although a few occur in the tropics.