Red speckled dun mayfly found near Friday Harbor

October 5, 2026

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A mayfly was observed on September 30, 2026, in the San Juan Islands National Monument near Friday Harbor.¹ Callibaetis species are multi-generational, producing up to three broods per year, with the final brood typically emerging in fall.¹ Late-September emergence of this pollution-sensitive mayfly reflects the seasonal decline in temperature triggering the third-generation hatch from nymphs that completed development over six weeks.¹

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