Friday, March 30, 2012

Isoperlas, Isoperlas, Isoperlas: Back to Sugar Hollow

The Perlodid stonefly Isoperla similis, one of several Isoperla Perlodids that I've only seen in two small streams in Sugar Hollow.   According to Beaty ("The Plecoptera of North Carolina," p. 24) this one is "relatively uncommon," and it's "collected from headwater Mountain streams and medium rivers during the winter and early spring." I do think of this small mountain stream as a "headwater" stream, even though there are smaller streams still that feed into it higher up on the ridge.

I. similis has a tolerance value of 0.8. and Beaty's description of the key features includes: "head brown with a pair of pale spots near labral suture, a pale M-shaped mark anterior to median ocellus and pale marks anterolateral to the lateral ocelli; abdomen brown with a light median longitudinal stripe and with a pair of faint submedian pale dots on each segment."  Let's have a look (best to click on the photo to enlarge it.)

The pale dots near the labral suture might show up even better in a second photo:

One more photo, taken in quite different lighting conditions (the sun was not very helpful today, peaking out through the clouds and then disappearing!)

Steven Beaty told me last year that the mountains in North Carolina and Virginia are richer in species of Isoperla Perlodids than anywhere else in the world.  And, you may recall that last spring I found two Isoperlas  in Sugar Hollow that even Beaty could not ID to the level of species (see the entries posted on 5/19, 5/21, 6/14, and 6/16)) -- both of those nymphs, by the way, were found in the stream that I went to today.  This is one of the two:

And today I was happy to see that this is a species that is a permanent resident here.  Look at this small version of the nymph in the photo above.  (Note the pale spot in the ocellar triangle, and the pale line that arcs between the rear ocelli.)

Finally, one more Isoperla in the insects we ran into today -- a very, very small Isoperla holochlora, even smaller than the one I found on Tuesday up at South River.  This is one of my favorite stoneflies, and I'm looking forward to watching them change as they mature through the spring.


Two other insects to highlight from today's venture.

1. A very nice common netspinner caddis -- Diplectrona modesta.

2. And the flatheaded mayfly that only hangs out in "pristine" headwater streams -- Maccaffertium meririvulanum.

(Where you go when you want to see really good insects.)

1 comment:

  1. Thanks, Bob.
    Ugly little buggers, aren't they!