Drunella spiny crawlers again -- but the common stonefly Perlesta is taking over the stream: Up to the Moormans

One of the better photos I've gotten of the spiny crawler Drunella tuberculata.  What a beauty!

I decided to look at the Moormans this morning.  I have a site that I visit right below the first bridge in Sugar Hollow.  I expected to see flatheaded mayflies, small minnow mayflies, and the common netspinner caddis.  I did.  But once again I saw a lot of Drunellas, D. tuberculata and D. cornutella -- two days in a row!  They were mostly in clumps of leafs and twigs, though I did find one cornutella just strolling along on a rock.  I photographed two D. cornutellas which turned out to be a male and a female.  Spiny crawler male nymphs have big red eyes just like we see with male small minnow mayflies.

male:

female:

I guess D. cornutella is more common than I had assumed.
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But the big story today -- Perlesta Perlids (common stoneflies).   I had forgotten how they "blossom" in a lot of our streams when we get into June.

I picked up 20-30 in a short time this morning -- most were in leaf packs.  I saw one A. abnormis Perlid and one I. holochlora Perlodid: everything else (stoneflies) was Perlesta.  Three features to look for: 1) anal gills are present; 2) the abdomen, actually most of the body, often looks speckled; and 3) the setal row on the occiput is sinuate with gaps.  (See Steven Beaty, "The Plecoptera of North Carolina," p. 19)

I had also forgotten that Perlestas are voracious predators.  I found a nice, fully mature Plauditus dubius small minnow mayfly this morning that I was sure would make a nice photo: one that looked a lot like this.

I eventually found it in my tray -- well, what was left of it -- in the mouth of that innocent looking Perlesta in the photo above!  Perlestas, by the way, are "univoltine" having a one year life cycle.  That's why we only see them at this time of year and watch them mature in 2-3 months.  Very pretty when they mature.

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One other insect that I don't see all that often, but one which is fairly common at this site in the Moormans -- a Polycentropodidae, "Trumpet-net maker" caddisfly larva.

The muscle scars on the head are very distinctive.  This one, like all of the Polys I've found, was Polycentropus in terms of the genus.   It's the "X" on the anal proleg that gives that away.

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Another surprise at Buck Mt. Creek: the spiny crawler Drunella cornutella

This is the Drunella species I was hoping to find at the upper Doyles river two weeks ago, since, until this morning, that's the only place where I had seen it.  Drunella cornutella is "slim and trim" compared to the other Drunellas we see in this stream: Drunella walkeri and Drunella tuberculata.
The striking feature -- the "long conical, semilunar lateral frontoclypeal projections" (Beaty, "The Ephemeroptera of North Carolina," p. 25).  These.

This is another taxon -- along with things like roll-winged stoneflies, net-winged midges, and green stoneflies (genus Alloperla) -- that I just don't expect to see in this stream, at least not this far down from its source.  The tolerance value is 0.0.  For a full run-down of the diagnostic features of D. cornutella, look back at my posting of 5/27/12.   Here are more photos.

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I saw a lot of Drunellas today, most were in the moss and grass on the tops of rocks out in the stream.  All of these were the common species I see at Buck Mt. Creek -- D. tuberculata.  I took photos of two of them.  The first corresponds to the colors that I normally see; the second is one that's fully mature -- deep rich colors and black wing pads.  The thorax and legs were the color of wine.

#1

#2

But without any question, the nymph of the day in terms of big numbers was the flatheaded mayfly Epeorus vitreus (TV, 1.2).   All over the place at the moment -- just turn over any big rock and you'll see them.  But, you've got to be quick if you want to get one -- they don't wait around to be stared at!

The vein pattern on the gills is much more pronounced than that of Epeorus pleuralis.  But the key feature to see for ID is the "four irregular pale spots on the anterior margin of the head, two submedial and two sublateral."  (Beaty, "Ephemeroptera," p. 17)  These.

Keeping the legs and gills intact on these nymphs -- what I always want for my pictures -- is a real challenge.
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The only stoneflies I'm seeing in a lot of our streams at the moment are Isoperla holochlora (Perlodid) and the genus Perlesta common stone.

And the only mayfly I saw today was a tiny, tiny, male Plauditus dubius (two tails with medial banding).  Also a tough subject for the guy holding the camera.

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But I was so happy to see D. cornutella.  Beaty says that it's "common," but that does not seem to be true in the streams that I visit.  Size: 7 mm.

Getting a start on the Small Minnow mayflies of Summer: Powells Creek

I think of summer as "Baetidae" season -- the season of the small minnow mayflies.   Of the 11 small minnow species I've located so far, only 3 -- Baetis tricaudatus, Heterocloeon amplum, and Plauditus dubius -- show up in the winter, the rest are around from late spring through the fall.  The "rest" are Acentrella nadineae, Acentrella turbida, Baetis flavistriga, Baetis intercalaris, Baetis pluto, Heterocloeon curiosum, Heterocloeon petersi and Iswaeon anoka.  Together, they produce those wonderful "Blue-winged olive" hatches that occur on cloudy days in late summer and fall.

So far this spring, I've only seen a few small minnow nymphs, all of them B. intercalaris, one of the most common Baetids we find in our streams.  Normally, I see quite a few in April and May, so where have they been?  The high water might be a problem since they can't "cling" to the rocks like the flatheaded mayflies, or maybe I've been spending too much of my time focussing on the Perlodids.  But today I was determined to find some small minnow nymphs, so I went to Powells Creek in Crozet where I've found a lot of them in the past.

And I found some; in fact I found three different species -- Acentrella nadineae (that's a small one, 3 mm, in the photo at the top of the page), Acentrella turbida (also small, 3 mm), and a small Baetis intercalaris nymph.  So, the season begins.

Photos:

1. Acentrella nadineae.  I found quite a few, and they were various sizes: the smallest, 3 mm, one that was about 5 mm and one that measured just about 6.  Mature nymphs run 5 - 5.8 mm. (Beaty, "The Ephemeroptera of North Carolina," p. 4.)   The orange/red markings on the thorax and terga makes it easy to identify this one.

It was another morning when the sun disappeared just as I got to the stream, so my photos sure aren't the best.  Here's a good A. nadineae photo that I took in the fall of last year.

2. Acentrella turbida.  I found 2 or 3, all of them small.  This one was 3 mm.  The A. turbida thorax is broad, and when they swim around in my tray they often flip up the back of the abdomen and the tails.  Not easy to photograph this one.

3. Baetis intercalaris.  Only 5 mm, but they're only 5-6 mm when they're fully mature.

Note the dark bands at the base, mid-point, and tips of the cerci (the tails).  They show up even better on this mature nymph that I found in September last year.

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I always enjoy the small minnow season.  The Rivanna River is a good place to find various species.
Just have to wait for the water levels to drop.
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And yes -- they're here in big numbers: very, very noisy!  Have to get some photos since I can't be sure I'll be here to see them again in 17 years.  Cicadas.

The flatheaded mayfly Epeorus fragilis: making the case

Yes: the flatheaded mayfly I found yesterday at South River was, indeed, Epeorus fragilis.  I feel safe in making this identification even without confirmation from Steven Beaty based on 1) more careful study, and 2) the matching photo of E. fragilis posted by Donald Chandler (http://pick4.pick.uga.edu/mp/20p?see=I_DSC95&res=640).  So let me go into a bit more detail.

I want to begin with what I hope is a clarification.  According to Beaty ("The Ephemeroptera of North Carolina," p. 17), E. fragilis is part of the "Epeorus pleuralis group."  Under "Epeorus" (the genus), here are the distinctions he makes:

I. Epeorus pleuralis group:
   1. E. fragilis
   2. E. pleuralis

II. Epeorus vitreus group:
   1. E. dispar
   2. E. subpallidus
   3. E. vitreus
   4. E. sp.1 

Personally, I think it is very confusing to use the same names (Epeorus pleuralis and Epeorus vitreus) for groups and species, and if I had the credentials I'd argue that that ought to be changed.  So, let me be clear: when I call something Epeorus pleuralis, I mean the species, and when I call something Epeorus vitreus, I mean the species.  I'd do away with naming the groups.
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All right.  On to Beaty's description.

(E. fragilis) -- mature nymphs < 6.7 mm; lateral margins of head capsule with abrupt transition near outer anterior corners of eyes, leaving eyes to hide much of the posterolateral margin of the head; ratio of head width to distance between antennal pedicels 2.11 - 2.45 (median 2.21); head with anterior margin mostly pale with a distinct "V" medially: abdominal terga 3-7 without small, paired, dark submedial spots.

1. The nymph that I found measured almost exactly 6 mm.

2. The ratio of head width to the distance between the antennal pedicels measured 2.2 -- that's almost perfect.

3. The abrupt transition from the union of eye and head margin is marked in the following photo as is the space where the eye and head margin coincide at the rear of the head and the side of the head (posterolaterally), thus "hiding" the posterolateral margin.  Also clear is the "V" at the front of the head.

Much less of the eye touches the head margin on E. pleuralis and E. vitreus nymphs.

E. pleuralis:

E. vitreus:

4. Finally, there are no "small, paired, dark submedial spots" on any of the terga that I can see.

If you want to see "dark submedial spots," look at the terga of the small minnow mayfly Heterocloeon amplum, especially terga 5 and 8-10.

Our microscope photo of the abdominal terga of E. fragilis also reveals something that drew my attention at the stream yesterday: two of the terga -- 7 and 8 -- are darker than all the rest.  And, the rear edge of terga 5-8 (the hind 1/4 of each of those tergites) consists of a dark band.

I wish I knew more about this new species -- state distribution, specific habitat, etc. -- but I've not been able to find that information.  We can certainly say that it is found in some of the very same streams in which Epeorus pleuralis is found earlier in the year, and it seems to coexist in those streams with E. vitreus (i.e. late spring/early summer).  At least that's the case at South River.  But it's a much smaller nymph than those other species.
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Is it a new Epeorus flatheaded mayfly -- "Epeorus fragilis"?

I went to South River this morning where -- you may recall -- I find lots of Epeorus pleuralis flatheaded mayflies every winter: they quite literally cover the bottoms of rocks.  E. pleuralis nymphs ought to be pretty well gone, so I was expecting to see their summer replacements, Epeorus vitreus.   I did see some, but none that would make very good photos.  But I continued to look.

Then I found the nymph in the photo above, which just looked a little bit odd: for one thing, the color didn't seem to be right for either E. pleuralis or E. vitreus, both of which tend to be brown or olive brown.  And on this nymph, terga 4-6 and 10 are clearly paler than the rest.

Remember that E. vitreus nymphs have four obvious pale spots on the front edge of the head.  They're easy to see in this photo.

Those are missing on Epeorus pleuralis, but on Epeorus pleuralis, there is a faint "V" at the front middle edge of the head.

But note that with both of these species, the space between the eyes at the back of the head is quite wide: i.e. the eyes hide very little of the posterior edge of the head.

Now have another look at our nymph.

And let's take a closer look at that head.

The eyes are much closer together at the rear of the head; there is a very distinct "V" at the front of the head; and the edge of the head is largely pale.

Let's see what Steven Beaty says about Epeorus fragilis (which is part of the E. pleuralis group).

(E. fragilis) -- mature nymphs < 6.7 mm; lateral margins of head capsule with abrupt transition near outer anterior corners of eyes, leaving eyes to hide much of the posterolateral margin of the head; ratio of head width to distance between antennal pedicels 2.11 - 2.45 (median 2.21); head with anterior margin mostly pale with a distinct "V" medially; abdominal terga 3-7 without small, paired, dark submedial spots.  Recorded from Deep Creek, GSMNP (DeWalt 2004).  ("The Ephemeroptera of North Carolina," p. 17)

I think the head of our nymph is a pretty good fit for that description.  What about the ratio of head width to the space between the antennae?  The ratio I found was 2.2.  That's right on the money.  And, there are no submedial spots on the terga.  One other thing, remember the size.  The nymph in our photos was 6 mm.  Both E. pleuralis and E. vitreus tend to be larger than that.  And, it's not that we're looking at an immature nymph: notice that the wing pads are already quite long.

So I wonder if I've found something new.  I'll want to run this one by Steven Beaty, and he might point something out that I'm missing.  Maybe it's just a "regular" E. vitreus or E. pleuralis.  But I like E. fragilis for the ID at the moment.   This is one on which I'll continue to work.
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Other photos:

1. A surprise: Isoperla nr. holochlora.  This differs from I. holochlora -- which is very common right now -- in that the pale area at the front of the head does not fully blend into the yellow line at the front of the head, and the abdominal "stripes" on I. nr. holochlora are not easy to see; they're indistinct.

2. I found two fully mature Peltoperlids (Roach-like stoneflies): deep, rich colors and black-tipped wing pads.  Beautiful!

3. And I saw quite a few Remenus, Perlodid stoneflies.  This was the largest one of the group.

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But the question of the day is -- is this Epeorus fragilis?

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Note:  I'm now pretty sure that this is, indeed, Epeorus fragilis.  Note Donald Chandler's photo of Epeorus fragilis at: http://pick4.pick.uga.edu/mp/20p?see=I_DSC95&res=640.  It's a match.  Common name of adult: Pale evening olive.