Saturday, April 13, 2013

Unexpected: Isoperla dicala (Perlodid stonefly) at Buck Mt. Creek

I confess that I've begun to think of Buck Mt. Creek as a little bit "common": we don't find the unique insects in here that we find in our small mountain streams.   But then I have a day like today when I'm reminded that this is a very rich stream in terms of the variety of insects that live here.  For a "non-mountain" stream, it's probably the best stream I explore.  And, it's especially rich in Perlodid stoneflies.  A quick reminder of the Perlodids I've found here so far: Clioperla clio, Diploperla duplicata, Helopicus subvarians, Remenus Bilobatus, Isoperla holochlora, Isoperla namata, and now -- Isoperla dicala.  Pretty impressive.

I have seen I. dicala only one time before -- at the Rapidan River in May of last year (see the entry of 5/11/12).   I did not expect to see it in Buck Mt. Creek.  My impression is that it is not at all common: North Carolina does not assign it a tolerance value having too little to go on.

Beaty ("The Plecoptera of North Carolina," p. 23) describes I. dicala in the following way:

I. dicala -- nymphs ~ 10mm; apex of lacinia broad although still narrower than base, with row of setae below subapical tooth.  We can see all of that in this microscope photo.

He continues: "pale marks anterior to median ocellus sometimes indistinct, sometimes with darker border; body and abdomen often speckled, particularly posterior segments; dark longitudinal abdominal stripes with very narrow pale borders."  I'd like a better description of the head markings: but the speckled body -- especially the abdomen -- and the narrow pale borders on the longitudinal bands are very clear in this photo.

From a distance, the abdomen looks a lot like that of I. namata, but the greenish hue of I. dicala and the head pattern set it apart.  Very exciting!


The rest of the insects that I saw this morning were as expected for this time of year.  Still, I got some super, super photos.

1. Look at this photo of the Perlodid stonefly, Diploperla duplicata.  The wing pads are spreading out from the body, and the pattern we see on the heads of the nymphs when they mature is clearly emerging.

2.  And a good pic of an Isoperla namata.

3. And, an excellent shot of a fairly mature Helopicus subvarians.

It's so nice when the insects "pose" in the dish and sit still!  I also saw a lot of flatheaded mayflies (M. pudicum and Epeorus pleuralis), a lot of spiny crawlers (E. dorothea), and a number of Nemourid stoneflies, genus Amphinemura.

The I. dicala nymph was still pretty small, still immature, as you can see in this photo in which it's swimming next to the H. subvarians nymph.


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