Thursday, December 1, 2011

Getting Bigger and Bigger: Large Winter Stoneflies at Long Island Creek

I apologies in advance for my photos today -- well I apologize for showing you dirty bugs!  We had over an inch of rain two days ago, and a lot of streams are still high and muddy.  But I thought if I went to a small stream, southeast of Charlottesville, I might find clear water to sample.  I chose to look at Long Island Creek near Palmyra in Fluvanna County; the water was high and a little off color, but there was no problem finding insects.  Still, from the high, muddy water, the leaf packs were all filled with dirt, and it tends to stick to the legs and tails of aquatic insects.  Alas!

The dominant taxon today -- as it's been in other streams lately -- was the small winter stonefly.  But, to my surprise, they were smaller than I've seen elsewhere, especially compared to those I'm finding now in Buck Mt. Creek.  (I thought south of town they'd be bigger.)  Not so with the "large" winter stoneflies -- Taeniopterygidae, genus Taeniopteryx.   I found quite a few big ones.  Note in the photo above -- and in the photos below -- how the hind wing pads have widened and spread out from the body and how the color of these nymph has darkened.

And another (these are three different insects).

The other taxon I found in large numbers today was the common stonefly, Eccoptura xanthenses.  This is the Perlid that inhabits small mountain streams.  It's the dominant Perlid in Powells Creek in Crozet and in the small streams I visit in Sugar Hollow.  Still, I'm not sure I've ever seen so many at once as I did today.  I must have seen 5-10, or more, in every leaf pack that I picked up, lots of different sizes.

Mayflies?  I found some pronggilled mayflies and one brushlegged mayfly and lots of small flatheaded mayflies.  But I had one pleasant surprise: I found a Maccaffertium vicarium flatheaded mayfly: we don't see these too often.

Dorsal view (dorsum):

Ventral view (sternum):

You may recall that I found one of these in the upper Doyles River on 10/10, and that it's one of the few Maccaffertium species that we can tell by the color pattern.  I quote from Steven Beaty ("The Ephemeroptera of North Carolina," p. 20): "wide dark bands on posterior margins of both dorsum and sternum of abdomen."  Those dark bands are very clear in the photos above.  This is a flatheaded species that is found in quality streams: the tolerance value is 1.5.  And Long Island Creek is a quality stream.

I found a couple of Green stoneflies (Chloroperlids) today; unfortunately my photos were not very good.  And I found one Perlodid stonefly, with very dirty tails, but I can't be sure of the genus.  I forgot to take a vial with me to the stream, so I couldn't preserve it for microscope study.  I think it might be a Diploperla -- but don't quote me on that!

Tomorrow -- back to small streams in Albemarle county.

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