Tuesday, November 8, 2011

Returning to the Small Streams -- and Finding Small Insects!

I'm finding it difficult now to go to mediocre streams -- and that means, unfortunately, most of the streams in our watershed.  In this part of Virginia, if we want to see good water and good insects we have to go to the Blue Ridge -- to the streams that flow out of the Blue Ridge and the streams that flow into those streams (tributaries), to streams at the base of the Blue Ridge, and to those that are still within sight of the Blue Ridge.  And right now, the good bugs that inhabit those streams are starting to show up in the leaf packs -- especially the Perlodid and Chloroperlid stoneflies.  I don't want to miss seeing them grow and mature from the very beginning.

So I went back to one of my "secret" tributaries to the Moormans this morning, where the Chloroperlid (Green Stonefly) was the dominant taxon.  That says a lot about the quality of this small mountain stream.  This is a very "intolerant" stonefly.  And if I'm right that the genus is Sweltsa, the TV is around 0.2 (North Carolina DWQ).    These were tiny, smaller than the one I found at the upper Doyles River last week, but I still managed some very nice pictures, and the distinctive "short tails," show up clearly in all of the shots.

In this one, note the small winter stonefly -- one of the few that I saw in this stream -- at the top left of the photo.

But I had another treat today: I found a very tiny Perlodid stonefly (about 3mm long), which I was, nonetheless, able to identify to the level of genus -- Diploperla.  Here it is.  (Hope you can see it -- remember to click to enlarge.)

And here it cozied up to a small crane fly larva.

How do we distinguish Perlodid from Chloroperlid?  Let's begin by looking at them side-by-side in this microscope view.  (By the way, when mature, the Perlodid will be much larger than the Chloroperlid!)

Two things are apparent at once: 1) the Perlodid's tails (the nymph on the left) are almost as long as its abdomen -- the Chloroperlid's tails, about 1/3 of the abdominal length; and 2) the abdominal shapes are not at all the same.

But you may recall that when the nymphs are this small, the real test to distinguish the two is the size of the terminal segment of the maxillary palp in relation to the preceding segment.  Here's a look at the labium of our Perlodid.

Note that the terminal segment is only slightly thinner than the penultimate segment.  Now look once again at the palps of the Chloroperlid I found last week.

Here the terminal segment is much thinner than the penultimate segment.  Perlodid and Chloroperlid -- that's how we tell them apart.

Now if you look back at the labium of the Perlodid, you can also see from that photo how we know that the genus is Diploperla: the terminal lacinial spine is very long, 1/2 as long as the lacinia.  So this is a tiny Diploperla that come April will look something like this.

Or maybe like this in May

Lots of changes to come over the winter!

The other stonefly that showed up in large numbers today was the Peltoperlid, the Roach-like stonefly, and I found one that had just recently molted -- the colors have not yet darkened.

But most of them looked like this.

You may recall that the pale dots on the pronotum are thought by some to be a sign of genus Tallaperla.

All in all a very nice day, and we are, at the moment, enjoying some beautiful fall weather.  It was so nice to be out in the cool, clean air, smelling of falling leaves, and to see so many beautiful insects in this beautiful mountain stream.  (Oh.  Also found Giant stoneflies, Common stoneflies (Acroneuria and Eccoptura), and flatheaded mayflies.)

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