Siphlonurus alternatus

(Say, 1824)

Northern Summer Mayfly

Siphlonurus alternatus is a primitive minnow mayfly with a Holarctic distribution spanning North America and Europe. The is , as and emerging as between May and August. Larvae inhabit deep pools in rivers, streams, and calcareous lakes, where they feed on fine particulate organic detritus. Adults emerge during daylight hours, with males forming swarms at dawn and dusk.

Pronunciation

How to pronounce Siphlonurus alternatus: //sɪfləˈnjʊrəs æltərˈneɪtəs//

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Identification

As a member of Siphlonuridae, this has the characteristic primitive traits of the including well-developed mandibular tusks in nymphs and relatively simple wing venation. Specific diagnostic features for S. alternatus are not detailed in available sources. are likely medium-sized mayflies with the gray drake coloration typical of the .

Habitat

Deep pools in rivers and streams; calcareous lakes; middle reaches of watercourses from foothills to lowland areas.

Distribution

Holarctic: Canada (all provinces), northeastern United States, Alaska; Northern Europe including Fennoscandia; Britain and Ireland (northern regions with highly localized distribution).

Seasonality

emerge May through August; occurs during daylight hours.

Diet

Fine particulate organic detritus gathered from sediment; larvae are gathering/collecting .

Life Cycle

(one per year); overwinter; larval development occurs in aquatic ; emerge May–August.

Behavior

Large nymphs are capable swimmers, moving in short, darting bursts. Males swarm at dawn and dusk over light-colored substrate patches or floating vegetation such as water-lilies. The is likely eurythermic (tolerant of a range of temperatures).

Ecological Role

Larvae process fine organic detritus in freshwater systems; serves as prey for fish and other aquatic ; provide food for terrestrial during periods.

Human Relevance

Important to fly fishing as a member of the gray drake group; larvae and are significant food sources for trout and other sport fish.

Similar Taxa

  • Siphlonurus quebecensisAlso called early brown quill or gray drake; similar size, preferences, and angling importance; distinguished by earlier period and specific body segmentation patterns

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