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Lateral view of a Female Hexagenia limbata (Ephemeridae) (Hex) Mayfly Dun from the Namekagon River in Wisconsin
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.

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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Dorsal view of a Female Heptageniidae (March Browns, Cahills, Quill Gordons) Mayfly Dun from the Long Lake Branch of the White River in Wisconsin
This specimen is really strange, very different in form from any other mayfly I've seen. Unfortunately it was found alone crippled in an eddy and in pretty bad shape, and I couldn't find any others like it.
Taxon
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Site Editor
Plano, TX

Posts: 1311
Taxon on Jul 19, 2019July 19th, 2019, 7:10 pm EDT
Hi Jason-

I believe this female to be a spinner, rather than a dun, and is probably Spinadus simplex.
Best regards,
Roger Rohrbeck
www.FlyfishingEntomology.com
Troutnut
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Administrator
Bellevue, WA

Posts: 2758
Troutnut on Jul 20, 2019July 20th, 2019, 3:21 am EDT
Hi Roger,

That's an interesting guess and certainly seems to match the general body profile well. However, the color patterns on both the tergites and sternites are very different from those in the Spinadis simplex specimen you uploaded to bugguide.net earlier this year:

https://bugguide.net/node/view/1634542/bgimage

Another page on there led to this paper describing the first adult of Spinadis simplex:

http://www.ephemeroptera-galactica.com/pubs/pub_m/pubmccaffertyw1984p173.pdf

This characteristic seems especially relevant in the description of S. simplex, and doesn't seem to match this specimen: "The fore tibia is approximately three times as long as the tarsus, and one-third the length of the femur."

Another important one is, "The hind tibia is 1.16 times the femur length." They note this is also present to some extent in the nymphs.

Also, the shape of the subanal plate is pretty different and is noted as a valuable characteristic.

The paper also extensively describes the characteristics of an enlarged pronotum in S. simplex that doesn't seem to be present in this one.

Finally, the habitat is very different; this came from a smalls stream distant from any of the large rivers previously described as Spinadis habitat.

I still think this is a dun -- the wings are quite pale for a dun but not really hyaline like a spinner. My early photography didn't make this particularly easy to tell, but you can also make out setae on the margins of the wings in this picture.

The dun-spinner difference might explain some other differences including the leg proportions, but I think enough characteristics differ that it's probably not S. simplex.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist

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