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Photo#65589
mayfly - Rhithrogena flavianula

mayfly - Rhithrogena flavianula
Sierra City, Sierra County, California, USA
June 27, 2006
Found flying around a fast running rocky river.

Images of this individual: tag all
mayfly - Rhithrogena flavianula mayfly - Rhithrogena flavianula

Moved
Since I never measured this mayfly, and looking at the woodgrain it's laying on, I'd say that 14mm could be right.

Tom, more info...
I just finished reading McDunnough's 1924 description of Heptagenia flavianula, which is now Rhithrogena flavianula. His description seems to be a very good match for your specimen, except that the size--though quite large for Rhithrogena--is given as 14mm. R. flavianula is found in CA, and McDunnough's holotype and paratypes were collected in June (in CO).

Moved
The size is just an estimate, but I do remember quite a few of these swarming around a small stream, and they were quite large for mayflies.

Probably Heptageniidae
This one confounds me a bit. Are you sure about the size estimate? Two things seem to point to Rhithrogena: there does appear to be anastomosis of the veins in the stigmatic area, and the first tarsal segment of the foreleg seems very short. (I tried to check those traits with the larger image on your Pbase site, and they seem to fit.) However, a 20-25mm body would be larger than any Rhithrogena I know. The other problem is that the eyes are not truly contiguous on top of the head, but I believe that separation of less than the width of a lateral ocellus is the standard for contiguity.

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