Sorry no photo
While out fishing I came across a big drake spinner. I think it might be Litobrancha Recurvata. 2 tails 17 mm body length, front pair of legs darker than back two, olive abdomen, darker thorax. Collected August 28th, which is relatively late for Litobrancha. Also could be Hexagenia Rigida or Atrocaudata.
Anyone know if Litobrancha or the Late Hexs are present in Southeast Mn?
L. recurvata is recorded for MN, though the records appear to be from the northeastern corner. I haven't seen records of H. atrocaudata or rigida from MN, but they should probably be expected. They are recorded for WN and IA, with some records close to southeastern MN. H. limbata and bilineata are recorded for MN and are the most common Hexagenia species throughout most of the upper Mississippi River area. Although the peak of their hatch is usually earlier, stragglers of either species can be found into early September.
L. recurvata seems a bit unlikely. As you note, it is usually a fairly early emerger--around the end of May or beginning of June in my area, and probably June into early July in the upper Midwest. Although 17mm is just within the lower size range, this is the largest North American mayfly, with some specimens approaching 40mm. More significantly, I think you would have noticed the unusually dark wings. Even in the spinner stage, they have dark veins and a bronzy stain in the membrane of the wings.
If it was H. atrocaudata, you probably should have seen a dark border around the rear of the hind wing (though that dark border can also be found in some limbata, some rigida, and most bilineata).
Possibly. Is it a male? (Claspers will be present at the tip of the abdomen.) If so, and it's atrocaudata, the eyes should be quite close together on top of the head. Take a look at Jason's examples to see what I mean, and compare the dorsal and ventral markings to his: http://www.troutnut.com/specimen/472 http://www.troutnut.com/specimen/206
If it's a female, the eyes will be smaller and further apart, but the abdominal markings should still be similar, as in this female dun: http://www.troutnut.com/specimen/474
(Sometimes the markings might not be quite as dark.)
It's a female. The colors have likely darkened considerably as it's two days old and now dead. It does have some of the same abdominal marking as the second male spinner. So it is most likely Hexagenia Atrocaudata. Thanks for your help Gonzo.