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Hex Mayflies
Hexagenia limbata

The famous nocturnal Hex hatch of the Midwest (and a few other lucky locations) stirs to the surface mythically large Brown Trout that only touch streamers for the rest of the year.

Mayfly Species Drunella coloradensis (Small Western Green Drake)

This species is very similar to Drunella flavilinea. In areas where their ranges overlap, they can sometimes be found in the same streams. Allen and Edmunds (1962) say that Drunella coloradensis tends to favor colder water than Drunella flavilinea and that it may emerge as much as a month later.

Where & when

Time of year : July to early October

Preferred waters: Small streams

Altitude: High

According to Fred Arbona, this species requires streams which never exceed 60°F, and this limits them to small streams at high altitude.

Specimens of the Mayfly Species Drunella coloradensis

8 Nymphs
1 Male Dun
Male Drunella coloradensis (Small Western Green Drake) Mayfly Dun
The positive species ID on this dun comes from both the spinner that it (or possibly one other dun just like it) molted into and the overwhelming abundance of nymphs of this species in my kicknet samples from the same site.
1 Male Spinner
Male Drunella coloradensis (Small Western Green Drake) Mayfly Spinner
This spinner molted from this dun, or possibly one other dun I had in the same container that looked just like it.

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References

Species Range
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