Monday, February 14, 2011

Stream Reports: Powells Creek and Doyles River

Here's looking at you kid!  Finally, small minnow mayflies -- and lots of them at the Doyles River near White Hall.  Yes, fly fishermen, there will be a hatch of Blue-winged Olives in March!

With temperatures in the 60's today, I decided to look at two different streams to see if I could find anything new: and I did.  I went to Powells Creek near Crozet first -- but let me report in reverse and start at the Doyles.

I found a lot of small minnow mayflies (family: Baetidae) at the Doyles.  In fact, other than the black flies -- and there were large colonies of them, ugh! -- this was the dominant taxon in the searching I did.
And while there continue to be large and small winter stoneflies, and Perlodid stoneflies, in the leaf packs, all of the small minnows I found were on the tops and bottoms of rocks.

They were all genus Baetis.  How do we know?  There are only three small minnow genera with two tails (all of the others have three): Baetis, Acentrella, and Heterocloeon.  The difference is that the "Metathoracic wingpads" -- the "rear wingpads" -- even though they are tiny and finger-like, are visible only on genus Baetis.  I hope you can see the left metathoracic wingpad in the microscope photo that follows.

I also found one small flatheaded mayfly -- genus Epeorus.  This is one of the streams which supports that particular genus.  And I found a few small winter stoneflies and large winter stoneflies (both genera), all of them mature and colorful and ready to hatch (I also saw a lot of small and large winter stonefly adults in the air and on rocks).   One large winter stonefly, genus Strophopteryx, was really quite striking: it had brown stripes on the abdomen instead of yellow and green.  I have never seen this color combination before, though the "keys" do allow for it.

A thing of real beauty -- and notice the very dark-tipped wingpads, a sure sign of preparation for hatching.

One other thing of interest from the Doyles River.  I found two, large, Perlodid stoneflies, genus Clioperla, and put one in my tray for a photo.  Unfortunately, I put him into a cube (I was using an ice cube tray) in which there was already a small minnow mayfly.  He ate it!  Right in front of my eyes.  If you look closely, you can still see the little small minnow legs sticking out of the Perlodid's mouth!

Now back to Powells Creek, which, I believe I said once before, "never disappoints".  Four things of special interest.  The first is that although I found -- as usual --  a lot of Eccoptura common stoneflies in the leaf packs,  I also came home with a Neoperla!   This is the only stream in which I have seen this genera.  It is distinct from all other Perlids (commons) by having only two ocelli (little black dots) on its head; all the others have three.  Here's a picture of the head -- and then one of the entire nymph.  Note the thin line of hairs at the back of the head (the "occipital ridge").

The second thing I was excited to see at Powells was a new (this year) genus of Perlodid stonefly.  While I continued to find Diploperla Perlodids at Powells -- quite a few of them, and they're getting quite large -- I also found a couple of small Perlodids, genus Isoperla.   This is the genus we see a lot of in April and May when they're mature.   Their abdomens are very distinct with alternating light and dark colored stripes.

A third thing of interest -- I found a wee little Spiny Crawler mayfly, which I never saw until I looked at everything at home under the scope.  Here he is side-by-side with a fully mature spiny crawler.

The mature nymph is about 1/2" long -- so that little guy is really small!  Still, with greater magnification, we can see the gills on top of the abdomen.

One more photo.  I'm starting to see quite a few Uenoid case-maker caddisflies that have now entered pupation.  When they do this they tend to huddle together in a group on a rock.  This is a small group: I've seen 30-40 cases stacked closely together in a space of, say, 4"x4".

There are still a lot of Uenoids crawling around on the rocks -- not all of them have gotten the genetic signal that it's time for the "big change."

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