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Mayfly Species Rhithrogena hageni (Western Black Quill)

According to Fred Arbona in Mayflies, the Angler, and the Trout, this is an excellent hatch and one of the most common fast-water mayflies in the West.  

Where & When


Region: West

Time Of Year (?): July to August

Preferred Waters: Large rivers and streams

Altitude: Above 5,000 feet
There are conflicting accounts of the hatch dates for this species. Caucci and Nastasi list it as a July-August emerger, but Knopp and Cormier speak of it hatching in the spring.

Hatching Behavior


Time Of Day (?): Late morning on warm days; early afternoon on cold days

The nymphs emerge on the bottom of the river and float to the surface as fully formed duns.

Spinner Behavior


Time Of Day: Late evening to dusk

The spinner falls are more important than the emergence. Knopp and Cormier give an unusually specific description of the conditions for a spinner fall in Mayflies: An Angler's Study of Trout Water Ephemeroptera :

Female spinners commence their fall during the evening or just before dusk, when air temperature has fallen to the low 60s F. If the air temperature drops below 58F, the spinner fall is often delayed until the next morning.

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