Friday, November 18, 2011

Stonefly Season

This is stonefly season.  I am seeing some mayflies -- mostly flatheaded mayflies, genus Maccaffertium, and in streams that have them, I'm seeing brushlegged mayflies.  But in less than a month I've seen, for the first time this season, small winter stoneflies, large winter stoneflies, green stoneflies, and Perlodid stoneflies -- four different genera.  What a treat to see all this new life in our streams, and to track them as they grow and mature.

On 10/25 (less than one month ago) I found my first small winters in the Doyles River, and I posted this picture.

The nymph in the photo at the top of the page is one of many small winter stoneflies that I found this morning at Buck Mt. Creek -- and note that it's almost fully mature.  Look at the colors and the rich patterns, and note how the wing pads are turning gray.   There will be small winter terrestrials flying around in the near future, perhaps even next week.  Small winter stoneflies go from youth to maturity in a very short period of time.  They show up in late October; most will be gone by the end of December.

Every small winter stone (Capniidae) that I've seen in our streams is genus Allocapnia.  Although North Carolina reports findings of two other genera -- Nemocapnia and Paracapnia -- Allocapnia is also the most common small winter that's found in that state.  How do we determine the genus?  It's all based on the shape of the rear wing pads.  I quote from Peckarsky, Freshwater macroinvertebrates, p. 66, "Metathoracic [i.e. hind] wingpads usually truncate [i.e. squared off] unnotched or notched on inner margin near tip."  Here's a close-up of the wing pads of the nymph at the top of the page.

Look at the rich patterns on the abdominal segments, the meso and meta thorax -- even the primary wing pads!  I think these rear wing pads are notched -- take a close look -- but I've certainly seen samples where the notches are clearer.   For example...

 Species?  I don't have a key that can help me figure that out.  It could be Allocapnia nivicola -- go to -- but I don't know that for sure.   Whatever the species, I was delighted to see one this morning that's so close to being mature.  And here are some photos of more of the small winters that I found today.

And a nice double:

While small winter stoneflies certainly dominated my findings this morning, I also found some large winters as well, and they too were much larger than those I found in this stream only two weeks ago (see the posting of 11/3.)

Taeniopterygidae, genus Taeniopteryx.  Note how the pale line that runs from the back of the head down to the start of the tails is now very clear.  And, I got a wonderful photo of the coxal gills -- which look a lot like "bean sprouts" -- that provide the sure key to identifying this genus.

Anyone can see those with a loupe, probably with the naked eye alone.  Once large winters reach this size, monitors should be able to identify them at the stream.

One other stonefly from my visit today.  This is a Perlodid stonefly -- the only one I saw -- genus Diploperla.  You may recall that I found a teeny one in a small mountain stream on 11/8.

The Perlodids I've seen so far are simply too small to ID at sight; it requires microscope work.
And, there are two things we see on this nymph that lead us to the Diploperla identification: 1) the "Posterior ends of [the] arms of [the] mesosternal ridge meet [the] posterior edge of [the] mesosternun separately,"  and 2) "[the] lacinial spine [is] long, 1/2 as long as [the lacinia]."  (Peckarsky, Freshwater Macroinvertebrates, p. 71.)   Here are the photos that back that up.



It's a beautiful day in central Virginia -- blue sky and full sun.  After three solid days of gray skies and rain, it was wonderful to get back to the streams.  With luck, I'll journey to the Rapidan River tomorrow to see how the "stonefly season" is progressing up there.

(By the way, as I've been writing this entry, the number of "page views" for this blog moved to 16,001.)

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