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The Specimen

Baetis (Blue-Winged Olives) Mayfly DunBaetis (Blue-Winged Olives) Mayfly Dun View 4 PicturesI'm guessing this specimen is in the genus Acerpenna because of the very sharp costal process (
The costal process of a Baetidae dun.
The costal process of a Baetidae dun.
Costal process: A bump or point sticking up from the front margin of an insect's wing, usually the rear wing of certain mayflies. It is sometimes called a costal projection.
on her hind wing. I'm guessing pygmaea because it is the most common species.

Editor note: Not Acerpenna. This is most likely Baetis. See comments on this male specimen for rationale. Also compare with the female specimen associated with it.
Collected July 1, 2005 from the Bois Brule River in Wisconsin
Added to by on April 22, 2006

The Discussion

TaxonJuly 1st, 2006, 10:54 pm
Site Editor
Plano, TX

Posts: 1295

My guess would be Baetis brunneicolor.

Roger Rohrbeck
TroutnutJuly 2nd, 2006, 7:20 am
Bellevue, WA

Posts: 2543
How come?
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist
TaxonJuly 6th, 2006, 10:45 am
Site Editor
Plano, TX

Posts: 1295

Oh, sorry. Just discovered your response. Because of the striking similarity of your specimen's fore wing venation to the that of Baetis brunneicolor portrayed in Leonard & Leonard, page 87, Fig. 51.

Here is your photo arranged for comparison purposes:

Roger Rohrbeck
TroutnutJuly 6th, 2006, 11:25 am
Bellevue, WA

Posts: 2543
Ok, thanks. I just looked at Leonard and you're right that the venation is strikingly similar (though not identical). They don't have very many other Baetis wings to compare to, though, so I'm hesitant to rule out the other species on those grounds.

The costal process on the hind wing is much sharper in this specimen than in the Leondards' drawing. I think that's a fairly important characteristic for this family and it's one reason I'm hesitant to call it Baetis.

Also, the Leonards show some intercalary veins on the hind wings of brunneicolor, which I don't see in this photo. That could be due to individual variation or bad focus in the photo, though.

The taxonomy of this whole family is such a mess right now. I really hope somebody publishes a definitive key to the genera soon based on something better than mandible setae and the like.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist
TroutnutSeptember 21st, 2006, 9:28 pm
Bellevue, WA

Posts: 2543
I'm even more confident that this is Acerpenna now that I've photographed an extremely similar specimen from upstate NY. The new female was associated with a male which I also photographed, and it keyed fairly confidently to Acerpenna in Merritt & Cummins.

I've fallen a bit behind on posting new pictures I've taken. I've got about 30 new specimens to put up, I think, including the Acerpenna pair. All that's coming ASAP.
Jason Neuswanger, Ph.D.
Troutnut and salmonid ecologist

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