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Female Isoperla fusca (Yellow Sally) Stonefly Adult Pictures

 The family ID on this one was a little bit tricky. Just going by the size, shape, and color, it looks like Chloroperlidae. However, the second anal vein of the forewing is does not appear to be forked, and the apical (Apical: Close to the apex; tip or end.) maxillary palpal segment is close to the length of the penultimate segment, both of which rule out that family. The position of the cubitoanal crossvein (Crossvein: Short cross-wise veins in an insect wing which connect the long longitudinal (length-wise) veins.) relative to the anal cell in the forewing -- touching it in this case -- indicates Perlidae (and it really doesn't have the "look" of Perlidae at all), but other characteristics, such as the metathorastic sternacostal sutures and lack of gill remnants, point to Perlodidae. That's the right answer. Moving on to Perlodidae, the key characteristics in Merritt & Cummins lead straightforwarly to Isoperla, and the species key in Jewett 1959 (The Stoneflies of the Pacific Northwest) leads to Isoperla fusca.

There is one caveat: That source does suggest a May-July emergence, whereas this one was collected in mid-September.


This stonefly was collected from the Yakima River on September 17th, 2020 and added to Troutnut.com on September 19th, 2020.

Mesobasisternum  Female Isoperla fusca (Yellow Sally) Stonefly Adult from the Yakima River in Washington
Mesobasisternum
Metabasisternum, backlit  Female Isoperla fusca (Yellow Sally) Stonefly Adult from the Yakima River in Washington
Metabasisternum, backlit
Metabasisternum, toplit  Female Isoperla fusca (Yellow Sally) Stonefly Adult from the Yakima River in Washington
Metabasisternum, toplit
Female terminalia, backlit  Female Isoperla fusca (Yellow Sally) Stonefly Adult from the Yakima River in Washington
Female terminalia, backlit

Recent Discussions of this Adult

Stuck on the family ID on this one -- any thoughts? 1 Reply »
Posted by Troutnut on Sep 19, 2020
Last reply on Nov 12, 2020 by Troutnut
See the caption to this specimen for the reasons why I'm not sure what family to place it in. In a nutshell, it looks like Chloroperlidae, seems to key to Perlidae, and doesn't look like Perlidae at all. I'm either missing or misinterpreting some key features or stumbled upon a specimen that violates a bunch of "usually" characteristics in the key.
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