Friday, March 25, 2011

The Rapidan River: Insects that Dazzle the Eye

I think that "color" is the word for the day, beginning with this brilliantly colored and wonderfully patterned Perlodid stonefly -- genus Yugus.  This is the first time I've seen this genus: what a beauty!
The find was unexpected: this is a genus I did not know we had in our streams.  Another look:

(The reddish orange marks at the base of the wingpads, by the way, are eggs that are stuck to the body.
Was he in the process of eating them?)

Once again, I lamented the fact that the Rapidan River is not in our watershed -- it flows through Madison County and empties into the Rappahannock.    The headwaters are in the Shenandoah National Park, and I like looking for bugs near the spot where fly fisherman park to head up the stream.  The insects are abundant, and they're the insects that live in high quality water.  The Yugus Perlodid has a TV of "0".

This is the only Yugus Perlodid I saw today, but I saw a lot of Isoperla Perlodids and one Diploperla Perlodid.  I also saw Giant stoneflies and Roach-like stoneflies and Common stoneflies -- genus Paragnetina.   This is the only stream in which I see this Perlid (common) genus, and it too is a very colorful nymph as this photo reveals.

The Isoperla Perlodids surprised me: they were bigger here -- more mature -- than any I've seen to date in other streams.  In this one, the wingpads are almost fully developed, and the brown stripes that run down the abdomen are already distinct.  I don't expect to see Isoperlas with their colors this marked until late April or May.

I saw four different families of mayflies: spiny crawlers, brushleggeds, flatheads (all Epeorus by genus), and pronggilleds.   The spiny crawlers I saw were all Ephemerella by genus -- but there were a couple of the very large, beautifully colored spinys that I've seen in this spot before.   The rest were all on the small side, but still nicely patterned.  Here are both types for contrast.

This spiny is in full "defensive" position -- you can see that another stonefly had just passed it by -- and it's "wingpads" are starting to look a whole lot like wings!

The river was loaded with Epeorus flatheaded mayflies, and a lot of them were also very big -- clearly getting ready to hatch.  As with small minnow mayflies, when flatheads approach hatching stage, they darken in color and the wingpads turn black.  Fly fishermen can expect to see "Quill Gordons" (our name for Epeorus nymphs and adults)  up here in the very near future.

I had another "first" today, in addition to finding that gorgeous Perlodid stonefly.  I found my first "Net-winged midges" (family: Blephariceridae) of the year.  I've been expecting to see them.  In the streams that I've sampled with StreamWatch, they are regulars in Buck Mt. Creek and the Doyles.  This is a midge with a very low tolerance value ("0"), and for some reason they like to hang out with black flies!  Go figure.  They are invariably close to, or mixed together with, maturing black fly larvae.  They are "scrapers" (sc) in terms of functional feeding group and "clingers" (cl) in terms of "habit".  They cling to rocks that they're scraping with little "suckers" that are found on the bottom of the head and each abdominal segment.  Here are the best live shots I could get (they're pretty small) -- first dorsal, then ventral.

I'll close this report with one more look at that Perlodid stonefly: finding that was an experience I won't soon forget -- and it probably won't be very long before I return to this wonderful river.

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