Also found in: Dictionary, Thesaurus, Wikipedia.
Related to alderfly: Sialis lutaria, Fishfly
common name for a group of insects of the order Megaloptera, found throughout E North America. The adults may be 5 in. (12.7 cm) long; the male has mandibles half as long as the body. They are soft-bodied insects with a fluttery flight, and are largely nocturnal.
..... Click the link for more information. .