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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 58°F, the spinner fall is often delayed until the next morning.

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