I don't know for sure that this is Drunella tuberculata
, but that's my best guess for now.
It certainly has a different look and much more robust body shape from Drunella lata
duns I photographed a couple weeks earlier, so I doubt it's that species. Using distribution records to eliminate other choices narrows this down to Drunella tuberculata
or Drunella walkeri
Markings described for the abdominal sternites
of the male spinner of Drunella tuberculata
are suspiciously similar to those on this female dun. Also, this dun is 9.5mm long (my ruler pic isn't very good, but I'm basing this on measuring the real thing). The size range given in the old Allen & Edmunds keys for walkeri
females is 7-8mm, while tuberculata
is 9-11mm. For these reasons I'm sticking it in tuberculata
This is the only Drunella
mayfly I saw all day. I scooped it off the water as it emerged at around 7pm from a big Catskill tailwater.