Sunday, June 24, 2012
Heterocloeon curiosum at the Rivanna -- but Some New Small Minnow Mayflies as Well
I've been having trouble finding small minnow mayflies in most of the streams that I visit in the winter and spring: no problems today at the Rivanna. The Rivanna has been too high and off color for me to explore until now. But I could finally get in and look for some insects today. I saw three or four small minnow mayflies on the first rock I picked up, including the one in the photo above -- Heterocloeon curiosum.
This is a common small minnow in the Rivanna in summer; it's a species I hardly see anywhere else. You might recall from last summer that the distinctive trait of this species is the pair of forecoxal/procoxal gills. These:
Also distinctive is the dorsal pattern: most tergites are brown, with 4 and 10 being pale yellow. We have a good view of that in the photo below.
I can't say for sure that "sternal tracheation" -- note the gray tracheation on the mesosternum in the microsocope photo above -- is also a species characteristic, but it's something I normally see. Using size, forecoxal/procoxal gills, and sternal tracheation for definition, the three nymphs pictured below were also H. curiosum. But if that's true, I sure find the colors more than a little bit odd. (Well, number three might be all right.)
I think these require more work.
But I found more than H. curiosum this morning. Another small minnow that was easy to pick out by the tails -- a Baetis intercalaris.
And now we turn to the unknowns. I found three additional small minnow mayflies this morning that, so far, I have not ID'd, and I think they are three different species. Since I see no procoxal gills on any of them, they are probably Acentrella or Plauditus nymphs in terms of the genus. But at the moment, that's all I can tell you -- well, except that all three were small, 3-4 mm. Here they are.
Mystery Baetid 1: This one was fairly mature and had banded cerci. 4mm
Mystery Baetid 2: Cerci (tails) on this one were missing. 4mm
Mystery Baetid 3: The smallest of the lot -- only 3 mm in length.
The lab work on these may take me awhile. If I'm successful I'll be sure to post my results.
Finally, a special treat for me today: the first Calopterigidae of the season -- a "broadwinged damselfly."
I didn't keep it so I can't be sure of the genus. But the broadwingeds that I found last year were all Haeterina.