Wednesday, October 26, 2011

On vacation

(A large Baetis pluto small minnow mayfly, and a small brushlegged mayfly found yesterday in the Doyles River at Doylesville.)

I'm off to Portland, OR to visit my daughter for a few days -- returning to VA on 11/1/11.  So, I'll be back in the streams by the end of next week, posting new entries (I'm sure there will be pictures of "small" large winter stoneflies [Taeniopterygidae] by then.)

I continue to be gratified by the -- to me -- incredible response to this blog.  We just passed 13,500 hits in less than a year, with a daily high of 158 yesterday.  It makes me happy to know that there are so many of us, around the world, who want to learn as much as we can about aquatic macroinvertebrates and to enjoy how beautiful they are when we see them close up.

Bob Henricks

Tuesday, October 25, 2011

Now Playing in a Stream Near You: "Small Winter Stoneflies" (Capniidae)!

I spent the morning at the Doyles River in Doylesville, where I found the first -- for me at least -- small winter stoneflies of the season.  At this point they are immature and very tiny -- 3-4mm long, .5mm wide -- but we will be able to watch them grow and mature in November and December: most will hatch and be gone by the end of that month.  Before they hatch, they'll look something like this.  (Picture taken 12/4/2010.)

If you're out sampling right now, there are a couple of things that will help you identify this stonefly to family level -- though you should never make that call in the field unless you really know what you're doing.  1) The color at this time of year is pale yellow -- small ones are almost translucent.  2) With the long thin shape, they are "thread-like," and in some ways resemble large midges.  However, they never wiggle and squirm on the net or in a tray to the degree that we see with midges.  And 3) as is the case in the photo above, small winter stoneflies tend to "float" on top of the water in trays, not "sink."  Another photo in which the nymph is floating on top of the water.

But to be "certain" of your identification, you have to look at these in the lab.  There are three features that you want to find.  1) "Look under the hood" at the labium.  There should be no "notch" between the glossae.  Even with these tiny nymphs, we can clearly see that the glossae (g) directly parallel one another.

2) And this is a tough one, running along the outer edge of abdominal segments 1-9 is a dark line -- a "fold." This is called the "pleural fold" or "ventrolateral fold," or "membranous fold," and that it extends from segments 1-9 helps us to distinguish Capniid nymphs from Leuctrid (Rolled-winged) nymphs, where the pleural fold only runs from segments 1-4.

3) The hind wing pads on Capniid nymphs are stubby and short (truncated) while the front wing pads are slender and long.  On more mature nymphs, by the way, this is a feature you can see with the naked eye -- or at least with a loupe.

On a mature nymph they look like this:

So there you have it, we're off and running -- the winter stoneflies are here!  And here's what they look like when they're really tiny.

But I found a second sign that the winter season is here.  I found two young Perlodid stoneflies -- also light in color.

Can we determine genus identification?  We can certainly narrow it down.  They're either Isoperlas or Clioperlas, and we know that because, 1) the tops of the mesosternal "Y" ridge point up, they don't go up and then point back down.

And 2) the lacinia of the maxillae have two large spines at the top with additional spines/hairs to follow, and they're rounded from the top to the base.

That brings us to Isoperla or Clioperla, and the key thing then becomes colors and patterns.  It's simply too early to "see" what we have to see to decide between those two genera.  But my money's on Clioperla.  And that's because we see Clioperla much sooner than we see Isoperla, and the key feature for Clioperla ID is that most of the head, from the eyes up to the dark tip at the end, is a light colored yellow.  Like this.

I think that color pattern is already starting to show on the two nymphs that I found today.

I found a lot of flatheaded mayflies today, and a fair number of crane flies.  But the last thing of interest that I found was again some small minnow mayflies.  I found  one small Acentrella turbida nymph, the first that I've seen in this river.  But the surprise of the day -- two more, beautiful Baetis pluto nymphs!
I'll end with those pictures.

Acentrella turbida

Baetis pluto

Oh, and I saw a number of brushlegged mayflies.

It's great to see a new season beginning.


The Doyles River at Doylesville.

Saturday, October 22, 2011

Photos: More Surprises at the Rapidan River

You may wonder why I spend so much time at the Rapidan River in Madison County, but it's really quite simple.  1) The insects here are prolific: I never have to hunt around looking for the odd mayfly or stonefly; 2) I find insects here that I find nowhere else -- quality insects; and 3) the location is right at the base of the Blue Ridge, and it's a beautiful drive -- the last 10-15 miles anyway.

On September 13th (you can look back at the entry) I was surprised by some of the insects I found in this river; the same was true today.  And we may as well begin with the photo at the top of the page.  On the left is a pronggilled mayfly (genus Paraleptophlebia); on the right a small minnow mayfly, Baetis pluto.  I haven't seen Baetis pluto since June 19th at Buck Mt. Creek (you might want to look back at that entry).

I did not expect to see prong-gilled mayflies this early, and they were all over the place -- very small, crawling around in the leaf packs.   This is a mayfly that we see in very few streams, but the Rapidan is a good place to look.  It has very unusual gills -- they look like "tuning forks".  Here are some photos: the "forked/pronged" gills are very clear.

On the small minnow mayfly -- at the stream, I was quite sure it was Baetis intercalaris; I found some here on my last trip.  I didn't realize that it was, in fact, Baetis pluto until I downloaded the pictures.  The
pattern on the head gives it away (it appears to be longitudinally striped -- alternating light and dark bands), and very obvious from the photos is the abdominal pattern: tergum 5 is pale in color, 6 and 7 are dark.  Have a look (and look back to the nymph that I found on 6/19).

And a side view,

So, I found some nymphs of this species that were nearly mature in June, and now here's one that is nearly mature in October.   Does that mean that this species has two hatches a year?  I can't tell for sure since my samples were found in two different streams.

More nice surprises today.  On September 13th, you may recall, I found a small Perlodid stonefly, genus Isogenoides, the first Isogenoides I've seen in Virginia.  Found another one today, and it's noticeably bigger than the one I found in September.  The species is Isogenoides hansoni.  Keys to species ID include, 1) the dark banding on the anterior and posterior edges of the abdominal segments, 2) the pale "M" shape on the head, and 3) the pale yellow dot between the lateral ocelli.

And at home with the microscope, I got some excellent photos of the morphological features used for genus identification -- 1) presence of submental gills, and 2) on the mesosternum, the median ridge extends to the transverse ridge.

I expect to see really tiny Perlodids in the other streams I explore by the end of this month or in early November.  But they'll be different genera: Clioperla or Diploperla are normally the first two that we see.

I also found, on 9/13, a really small spiny crawler, the beautiful nymph that will mature here sometime in late winter -- Ephemerella subvaria.  I found two more today, and they too were quite a bit bigger than those that I found here last month (look back at the post of 9/13).   A couple of photos of this colorful insect.

They're simply amazing.

Just three more things.

1) A Giant stonefly -- this one was well over an inch long.  They really are "formidable" looking critters.

2) A fair-sized free-living caddisfly larva.  (So, they're back.)

3) And, an Odontocerid (Strong case-maker caddis), genus Psilotreta.  I knew they were in here: it was just a matter of time before they showed up.

So another delightful day at the Rapidan River.  I'll be heading back there next month -- who wouldn't go?!

Below: The Rapidan River in autumn at the entrance to the Shenandoah National Park.

Friday, October 21, 2011

Photos: Fall Insects in the Moormans

I want everyone to really appreciate the photos that I took today since I had to drive 30-40 miles out of my way to get them!

On a beautiful day in Virginia -- sunshine, blue sky, cool temps, white puffy clouds -- I decided to head up to the Moormans.  I wasn't really surprised by the insect life that I found: small minnow mayflies (Acentrella turbida -- the species I expect to see here in the fall), netspinners and fingernets (a couple of each), tiny flatheaded mayflies and tiny brushlegged mayflies, a "junior league" hellgrammite, a fair sized Giant stonefly, and lots and lots of common stoneflies (Acroneuria abnormis).  I turned over a leaf pack that must have had at least 6 Perlids crawling around: I picked up the prettiest one for a photo.  I also hoped to get shots of the small minnow mayflies and the Giant stonefly.

I got all set up -- and the sun went under some clouds.  Waited, waited.  But it wouldn't come out.  So, I loaded everything up and drove in the direction where the sun seemed to be shining the most -- south to Crozet.  Got there, good sun, stopped and set up.  The sun went under the clouds!  Anyway, the third time I stopped -- on Ivy Road heading back to Charlottesville -- I finally got some photos.  They include some of the best pix of Acentrella turbida small minnow mayflies I've taken this fall.  So, here we go:

1) Here are two additional shots of the small minnow mayfly at the top of the page.  This is a real beauty.

2) A second Acentrella turbida small minnow mayfly -- but note the different colors.

3) Two shots of the Giant stonefly.  The insect on its back in the one photo is -- I think -- a very small Coenagrionidae (Narrow-winged Damselfly)!

4) A common netspinner -- genus Hydropsyche -- with unusual colors, not the drab green that we so often see.

5) Our beautiful Perlid stonefly -- Acroneuria abnormis.

6) And, an unfortunate meeting of the Perlid and the common netspinner.  And, yes, he/she ate the whole thing!

So, I got to see more of the countryside than I had planned, but good photos always make it worthwhile.

Thursday, October 20, 2011

Revisiting Peltoperlids (Roach-like Stoneflies): The Question of Genus

A friend of mine contacted me yesterday, asking how I had determined that the Roach-like Stoneflies that I've found in our streams are genus Tallaperla.  She also enclosed a photo of a Peltoperlid she had just found which -- like the nymph in the photo above -- had very clear "dark pigment spots located lateral to [the] ecdysial suture on [the] meso- and metanota" (Stewart and Stark, Nymphs of North American Stonefly Genera, p. 292.).  Those spots are a defining characteristic of the genus Peltoperla -- they are not found on Tallaperla nymphs.

Well, what to say?  Clearly this was one of those places where I had reached a hasty conclusion without doing my homework.  In my defense, I was following the key in Peckarsky, Freshwater Macroinvertebrates, p. 62) which does not distinguish the two genera.  But it was time to revisit this issue.  So I turned to more detailed sources of information, consulting, specifically, 1) Stewart and Stark (the book mentioned above, pp. 292 --- 306) and 2) Merritt, Cummins, and Berg, ed., Aquatic Insects of North America, p. 318.  In the latter we read: Peltoperla -- "Four paired, light-colored round spots on pronotum; paired dark pigment spots on meso- and metanota"; Tallaperla -- "Pronotum without paired, light round spots; prominent dark spots absent from meso- and metanota."

Stewart and Stark, of course, go into much greater detail, noting that there are three Peltoperlid genera that inhabit Appalachian ("our") streams: Peltoperla, Tallaperla, and Viehoperla.   We can rule out Viehoperla for the nymphs that I've found.  Number one, because it is not attested in the state of Virginia (though clearly, that's not conclusive).   But number two, because the thoracic gills on Viehoperla nymphs are single, but they're double on the other two genera.  All of the nymphs that I've found have "double" gills (see the picture above).  (Viehoperla is discussed in detail, and fully illustrated, by Stewart and Stark on pp. 302-306.)

On the genus Peltoperla, Stewart and Stark (p.292) make the following points: "Diagnostic Characters: (1) roachlike habitus, (2) gills absent on prothorax, but PS2 and PS3 [those at the base of the meso- and metanota] double, and (3) dark pigment spots located lateral to ecdysial suture [the line running down the middle of the back] on meso- and metanota."  They continue, "The other Appalachian genera Tallaperla and Viehoperla also have the general roachlike habitus, but Viehoperla nymphs have gills PS2 and PS3 single, and Tallaperla nymphs lack the dark meso- and metanotal pigment spots."  In  describing this genus elsewhere they add -- in agreement with Merritt, Cummins and Berg -- that these nymphs are "brown with circular pale markings on [the] pronotum."

So, for Peltoperla -- we should see "dark pigment spots" on the meso- and metanota and "four, paired, light-colored round spots on the pronotum."  However, it is my understanding that the light-colored spots on the pronotum are not always there, and that the presence or absence of these should not be used for identification.  (Private correspondence from an expert with the North Carolina Division of Water Quality.)

All of that to say, that I'm now convinced that the Roach-like stonefly pictured at the top of the page is genus Peltoperla.

So too is this one.

Both of these nymphs are from a small tributary to the Moormans in Sugar Hollow, the former found on 4/20, the latter (the photo directly above) on 6/13.  And note that the nymph in the photo above is fully mature, with dark wing pads -- ready to hatch.

Contrast that with the nymph in the following photo.

This nymph was found in the Rapidan River on 5/4.  It's also fully mature -- but there are no dark pigment spots on the meso- and metanota.   Not Peltoperla -- it must be Tallaperla.  So too is the following nymph found in the Rapidan River on 2/23.

So there you have it.  Clearly we have both Peltoperla and Tallaperla Peltoperlids crawling around in our streams.  Now, the streams where these different genera were found are really quite different in nature.  Though the one  -- the Moormans trib -- is small and drops sharply down the side of a mountain, the other -- the Rapidan -- is a wider stream with reduced gradient in the areas where I sample.
Still, they both make good habitat for Peltoperlids: clean, cold, rocky water in forested land where the stoneflies can find lots of leaf packs (that's where they like to live).

One final point.  Though I cannot see any "paired, light spots" on the pronota of the Peltoperla nymphs in the pictures above, I can make them out, using my microscope, on a small nymph that I had preserved.

Maybe they're just harder to see when a nymph ages and darkens in color.

So we've learned something, thanks to my friend who enjoys the work of genus and species ID as much as I do, and who has a very good eye for detail.

Additional note:  From what we have read, our Peltoperlas are probably Peltoperla arcuata and the Tallaperlas are Tallaperla maria.  For more information on the types of streams in which these species ae found, see: