Alderflies

Alderflies (Family Sialidae) are large, sluggish insects that anglers often misidentify—larvae resemble small hellgrammites, while adults are commonly mistaken for oversized, dark caddisflies. Larvae are dark brown to black, thick-bodied, and slightly flattened, with short lateral filaments along the abdomen. They live buried in silt, leaf litter, and soft substrates in ponds and slow-moving rivers, developing over one to two years as aggressive aquatic carnivores.

Adults appear in early summer and are distinctly dark, ranging from deep brown to charcoal black, with long antennae and smoky, opaque wings held roof-like over the body. They are weak fliers and spend most of their brief adult lives clinging to streamside vegetation, logs, and rocks. When disturbed—or during mating activity—adults frequently fall onto the water, where they struggle and drift. If fish are rising and alderflies are swarming around you, it’s a strong indicator to tie on an alderfly or hellgrammite-style imitation and fish it tight to banks and slower edges.

Curated by the IdentaFly fly fishing team.