Family Sialidae: Alderflies

Adults: Adult alderflies are 10-15mm long with black or yellowish, elongated, flattened bodies. They have four dark-colored wings that are held tent-like when at rest. Their antennae are threadlike and about half as long as body.

Larvae: Larval alderflies grow to a maximum of 30mm. A single feathery tail-like filament on the end of its abdomen is diagnostic for separating Sialids from Corydalid larvae. Abdominal segments 1-7 each have a pair of segmented filaments projecting laterally. The topside of the larvae is usually patterned and reddish brown to yellow in color.

Habitat: Larvae occupy streams, rivers, or lakes with soft substrate. Larvae burrow into substrate. Adults can be seen near the hatch site flying mid-day but stay perched most of the time on vegetation.

Ecology: Larval alderflies are predators in aquatic environments with soft bottoms and little or no current. They eat insects and other invertebrates. Abdominal filaments serve as gills. When leaving water to pupate, respiration is accomplished via spiracles in abdominal segment eight. Larvae are an important food source for fish and predatory aquatic insects. The adults do not fly well, and spend much of their time crawling over the vegetation. This secretive habit makes finding adult alderflies a special treat. Acoustical signals, produced by abdominal vibrations, are used to find mates. Adult alderflies do not feed. They respire via thoratic spiracles.

Reproduction: Alderflies undergo complete metamorphosis (four developmental stages: egg-larva-pupa-adult).Females lay eggs in masses on leaves or branches near the water. Upon hatching the larvae crawl into water where they feed and molt several times (about 10 molts before pupating) over a period of several years. They leave the water to pupate. The pupae overwinter in chambers dug into soft shoreline sediment and litter near the water?s edge. The adults emerge during late spring or early summer to mate and lay eggs, and live for only a few days.