Friday, January 27, 2012

Rapidan Riches: The Uncommon Taxa

I feel like I've spent most of the winter so far either waiting for sun, or waiting for the rivers to clear.
Today, we have blue sky and sunshine, but after rain overnight and a downpour this morning our rivers look like chocolate milk.  So, let me post a set of photos that I've been compiling.

I sample the Rapidan River in Madison county right where it flows out of the Shenandoah National Park.
It's a special stream, and I'll tell you why: I've found taxa there -- stonefly nymphs, mayfly nymphs, and caddisfly larvae -- that I've seen nowhere else in all of the streams I explore.  (The same is true for the tributaries to the Moormans River --  which are headwater streams -- and one of these days I'll write about them.)  So, let me go through the list of these "uncommon taxa," showing some photos, and noting the tolerance values for each taxon as posted in the recent list of tolerance values put out by the North Carolina Department of Water Quality (available on their website).

1. The Common stonefly (Perlidae), Paraganetina immarginata.  That's what's pictured in the photo at the top of the page, and I think it's one of the most spectacular insects, in colors and patterns, that I've yet to see.  Tolerance value: 1.1.  Another picture:

2. The Perlodid stonefly (Perlodidae), Isoperla nr. holochlora (i.e. it's "close/near" to I. holochlora, but not quite the same).  Tolerance value: 0.0.  Two photos:


3. The Perlodid stonefly, genus Yugus (arinus?  bulbosus?).  Tolerance value: not enough specimens found to determine a tolerance value (i.e. it's seen only rarely).   To date, I've only seen one.

4. The Perlodid stonefly, Isogenoides hansoni.  Tolerance value: not enough specimens found to determine a tolerance value.  I have only found immature samples so far: I hope to find a mature one so we can see it in its full colors.


5. The Perlodid stonefly Malirekus hastatus.  Tolerance value: 1.1.  This specimen is also immature.

6. The Spiny crawler (Ephemerellidae) mayfly, Ephemerella subvaria.  Tolerance value: not enough specimens to determine a tolerance value.  Perhaps the most colorful aquatic insect I've seen.


7. The Pronggilled mayfly (Leptophlebiidae), genus Habrophlebia.  Tolerance value: the only species listed is Habrophlebia vibrans, 0.3.

8. The Northern Case-maker larva (Limnephilidae), genus Pycnopsyche.  This is a genus I have seen elsewhere -- but only in a few, tiny, very good streams.  Pycnopsyche Limnephilids build cases that vary: each is unique.  Tolerance value of Pycnopsyche larvae in general is: 2.5.  Here are the two that I've found in this stream.

and, the "hot dog" case

9. And the other caddisfly larva that I've found in this stream that is truly "uncommon" is the Fingernet caddisfly genus, Dolophilodes.  Again, I have found this genus in a few other streams, but not very many.
Tolerance value for this genus: 1.0.


10. Since I've moved into the area of "seen elsewhere, but only a couple of times," let me add a final taxon:  the Giant stonefly, Pteronarcys biloba.  Tolerance value: 0.0.  The "hooked" corners at the front of the pronotum help us to ID this species.


It is very exciting to me, to find and photograph these kinds of insects -- exciting to find the "new" and the "uncommon."  (And note the very low tolerance values.)   Every time I get close to my "spots" on the Rapidan River, I tingle in anticipation -- "What will I find today?"

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