any of various neuropterous insects of the widely distributed group Sialoidea, such as Sialis lutaria, that have large broad-based hind wings, produce aquatic larvae, and occur near water
alderfly in American English
(ˈɔldərˌflaɪ)
noun
any of a family (Sialidae) of weak-flying neuropteran insects found near running water and having aquatic larvae that are often used as fishing bait
Word origin
alder + fly2: prob. so called because they inhabit alders along shore