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Lateral view of a Male Baetis (Baetidae) (Blue-Winged Olive) Mayfly Dun from Mystery Creek #43 in New York
Blue-winged Olives
Baetis

Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.

Dorsal view of a Glossosoma (Glossosomatidae) (Little Brown Short-horned Sedge) Caddisfly Larva from the Yakima River in Washington
I caught this tiny larva without a case, but it seems to key pretty clearly to to Glossosomatidae. From there, the lack of sclerites on the mesonotum points to either Glossosoma or Anagapetus. Although it's difficult to see in a 2D image from the microscope, it's pretty clear in the live 3D view that the pronotum is only excised about 1/3 of its length to accommodate the forecoxa, not 2/3, which points to Glossosoma at Couplet 5 of the Key to Genera of Glossosomatidae Larvae.
27" brown trout, my largest ever. It was the sub-dominant fish in its pool. After this, I hooked the bigger one, but I couldn't land it.
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Stenonema femoratum (Cream Cahill) Mayfly Nymph Pictures

This one had a hitchhiker I didn't notice at first.

Stenonema femoratum (Heptageniidae) (Cream Cahill) Mayfly Nymph from Mongaup Creek in New York
This is the picture that shows why this is Stenonema instead of Maccaffertium.  The main gills are rounded rather than truncate (square-ish) and the last, thread-like pair of gills is visibly tracheated (that little stripe through the center).  Those characteristics distinguish Stenonema femoratum.

Stenonema femoratum (Heptageniidae) (Cream Cahill) Mayfly Nymph from Mongaup Creek in New York
Stenonema femoratum (Heptageniidae) (Cream Cahill) Mayfly Nymph from Mongaup Creek in New York
Ventral view of a Stenonema femoratum (Heptageniidae) (Cream Cahill) Mayfly Nymph from Mongaup Creek in New York
Dorsal view of a Stenonema femoratum (Heptageniidae) (Cream Cahill) Mayfly Nymph from Mongaup Creek in New York
Ruler view of a Stenonema femoratum (Heptageniidae) (Cream Cahill) Mayfly Nymph from Mongaup Creek in New York The smallest ruler marks are 1 mm.

This mayfly was collected from Mongaup Creek in New York on May 6th, 2007 and added to Troutnut.com by Troutnut on May 18th, 2007.

Discussions of this Nymph

Not Stenonema femoratum
4 replies
Posted by Dewalt on Jun 12, 2013
Last reply on Jun 12, 2013 by Entoman
Only Stenonema left in North America (after taxonomic revision) is S. femoratum. The underside of the abdomen has rows of roundish dark spots at the lateral margins. This one does not.
Finally my "Stenonema" section isn't empty
2 replies
Posted by Troutnut on May 18, 2007
Last reply on May 20, 2007 by Troutnut
I've been looking for one of these for a while. After I realized that everything I was calling Stenonema had been renamed to Maccaffertium, the section for this once-popular genus was empty. Now with this one from a small stream in the Catskills I'm pretty sure I've got an actual Stenonema again.

I would welcome a verification from those of you with more entomological training, but it looks right to me.

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Stenonema femoratum (Cream Cahill) Mayfly Nymph Pictures

Collection details
Location: Mongaup Creek, New York
Date: May 6th, 2007
Added to site: May 18th, 2007
Author: Troutnut
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