Flies, Pacific Northwest
The alderfly is from the order Megaloptera. No fewer than 43 species of Megaloptera are known in North America with some 300 or so known species worldwide.
In general, this order of insect lives a rather short life and, interestingly, does not need to eat. This insect features long antenna though of differing design and large compound eyes. The alderfly has two sets of wings, these lying inward canted on the alderfly when it is at rest.
The alderfly begins life as larvae in water sources (water sources can be either calm or active). These larvae are noted for their length and multiple leg pairs as well as protrusions that appear as legs but serve as gills. The larvae lie in ambush and prey on other insect larvae and waterborne invertebrates.
The female Megaloptera lay their eggs in the hundreds, sometimes even thousands and will remain near water sources during the process. The hatchlings can then be born and slip directly into the water. Maturity is reached through multiple phases of metamorphosis.
The larvae are fully aquatic predators that feed on small aquatic invertebrates, such as snails, isopods, and insects. Alderfly larvae are an important food source for fish and predatory aquatic insects, such as dragonfly larvae.
The females lay eggs near water; upon hatching larvae crawl into water; larvae feed and molt several times over a period of several years until they leave the water to pupate for the winter underground near the water’s edge; adults emerge in early summer to mate and lay eggs, adults live for only a few days.
Like all aquatic organisms, alderfly larvae depend on clean water to live. The disappearance of wetlands and the pollution of rivers and streams are a potential threat to this and all aquatic organisms. Because of their sensitivity to pollution, alderflies are biological indicators of stream and wetland health.