Lynette-

The photo you emailed me, even though not of the quality you would want to post, clearly showed only two tails, so my belief that it was in family Leptophlebiidae based on its forewing venation has been seriously undermined. Hate to do this to you, but please move it back to mayflies. That way, someone else, who might recognize what it is, will be more likely to see it.

at that photo. I studied it closely. There is a very slight(and hard to see) dip about half-way back on the tails. I believe that the middle tail is mostly hidden between the other two. If that's not a middle tail, then the back tail takes a very unnatural bend. I also think I just see three tails coming from the end of the mayfly. I know the picture is terrible, but if you look long enough...

Lynette-

I believe you may be correct concerning the number of tails; just can't be certain.

Don’t think I can contribute anything to the ID, but might this be an example of abdominal bursting? That mechanism of parthenogenetic reproduction (in subimagos) was first described in a species of Eurylophella and is also reported to be found in an undescribed species (similar to Serratella) found on the Frying Pan in CO. The eggs are extruded in the same location as in this specimen through inflation of the midgut. David Funk, who did the research on Eurylophella oviruptis, might be interested in seeing this photo.