Acentrella nadineae small minnow mayflies -- tis the season: Up to the Lynch

I was looking for a particular insect this morning, and I found it shortly after I entered the stream -- the small minnow mayfly Acentrella nadineae.  Actually, with the exception of a single B. intercalaris, it's the only Baetid I saw, and it was around in significant numbers.

This is my favorite small minnow mayfly because of its spectacular colors.  The splashes of orange and red on the abdomen and the thorax are used for species ID, as are the unusual gills: "gills elongate, asymmetrical, and with basomedial pigmentation splotches."  (Beaty, "The Ephemeroptera of North Carolina," p. 4)  The oranges and reds are often muted on mature nymphs (see the second nymph pictured below -- the one with black wing pads), but the gills never change.  They're a dead give-away.

No question about it, the "splotches" of pigmentation do indeed run from the base of each gill to the middle.  And they are splotches!

A. nadineae was identified as a new species of small minnow mayfly in 2009 by McCafferty, Waltz, and Webb.  They noted that it had been found in southern and eastern Ohio and parts of North Carolina.   As I noted in my entry of 8/6/11, it's clearly in parts of Virginia as well: I've found it at the Lynch River, the Rapidan River, Buck Mt. Creek, the Doyles River, and Powells Creek, and I have no doubt that it's elsewhere as well.  With a TV of 1.9, it's relatively intolerant.

It's a beautiful insect -- but it's not easy to get a good photo of this one.  The nymphs never want to pause to pose.  So, of the 150 photos that I took this morning, I had 5 or 6 with which I was pleased.  Here you go.

In this photo, we have both a female and male (upper left, lower right).  As with most (all?) small minnow mayflies, the females are bigger than the males (6 mm vs. 5 mm).

And then there was this one, lonely, male Baetis intercalaris.

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While I've paid them little attention so far, the common netspinners are also appearing in force.  I took some photos of this Ceratopsyche alhedra this morning.

Oh.  The netspinner I found at the Doyles -- cream-colored body, light brown head -- was Ceratopsyche sparna.  Should have known that.

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And here is the nice set of riffles where I was looking this morning.

Serratella carolina/Serratella serrata: additional comments

The Serratella spiny crawlers that I found yesterday will be listed in our EPT list as "Serratella serrata/Serratella carolina."  This is why.

1. Serratella carolina was "synonymized" (i.e. equated) with Serratella serrata by Jacobus and McCafferty in 2003.   (Jacobus, L.M. and W.P. McCafferty, "Revisionary contributions to North American Ephemerella and Serratella (Ephemeroptera: Ephemerellidae)," Journal of the New York Entomological Society, 111 (4), pp. 174-193.)  Beaty tells me that NC has not yet accepted that equation,  but it very well may -- and soon.

2. The two species are distinguished in the following ways.

a) Both species have tubercles on the pronotum, but occipital tubercles are distinct on S. carolina while on S. serrata,  if they are present, they're "indistinct."  This is the photo I posted in the previous entry showing the tubercles on the nymph in the photo at the top of the page.

Beaty has looked at this photo and says that he can't really tell if the occipital photos are really "distinct," for that we would need a lateral view.  From what I can see with my microscope, those bumps don't really stick out from the head in a lateral view.  This is a call I can't make for sure.

b) S. carolina has tubercles on abdominal terga 3-9; S. serrata has them on 3-8.  As I noted yesterday, I "think" I can see them on tergite 9 on our nymph -- but I'm not really sure.  If they're there, they don't stick out in a prominent way, and -- and this is important -- in an article by Jacobus and McCafferty published in 2000 in which they demonstrate variation in the abdominal tergites for S. serrata, some of their figures (see 2 and 6) show "wavy" posterior edges on tergite 9.  (Jacobus and McCafferty, "Variability in the larvae of Serratella serrata (Ephemeroptera: Ephemerellidae)," Entomological News 111 (1), pp. 39-44.)  They look the same as those in this photo.

c) The caudal filaments of S. serrata have "intercalary hairs," those of S. carolina do not.  This is a tough one, but I do think I can see intercalary hairs on the tails of our nymphs.   They are too fine and too few in number for me to get a microscope photo -- but they are there.  Beaty tells me there are only a "few."

For all of these reasons, I've decided to label this species "Serratella serrata/Serratella carolina." If North Carolina (Beaty and the BAU) changes its mind on seeing the two species as one, I'll let you know.
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A new spiny crawler, Serratella carolina: a trip to the Doyles

My first stop today was Buck Mt. Creek where I was looking for small minnow mayflies.  I didn't find very much: a Gyrinidae (whirligig beetle), a Darner dragonfly, and various and sundry flatheaded mayflies including a nice Leucrocuta which I'll show you all in a moment.  But not doing real well at BMC, I decided to move on to the Doyles, where I fared much better.

Serratella is the genus of spiny crawler that we usually see in the summer, and I was happy to find two nymphs at the Doyles.  The species I normally see is S. serratoides, and I assumed I had found it again.  Still, I thought I should check everything out to be sure -- and it's a good thing that I did.

This morning's nymphs appear to be S. carolina, a species I have not seen before.   Here is Beaty's species description ("The Ephemeroptera of North Carolina," p. 31).

S. carolina -- nymphs 4.5-5 mm; maxillary palpi one apparent segment; tarsal claws with 5-7 denticles; occiput, pronotum and abdominal terga 3-9 with paired submedian tubercles.  Adults not known.  Found in Mountains only.  Relatively common.

One of my nymphs was 4.5 mm, the other was 5.  On the maxillary palpi, they do appear to have only one segment, but I do not yet have a photo to show that, and I can't tell how many denticles there are on the claws: just can't see that kind of detail with my microscope.

But, the tubercles on the occiput (back of the head) and the pronotum are clear.

So too are the paired submedian tubercles on the abdominal terga, though I will admit they are not easy to see on terga 3 and 9 in this photo.

Let me make two other arguments on this ID.  1) Of the four species of Serratella that Beaty describes, only S. carolina has tubercles on both the pronotum and head.  And 2) the other "common" species of Serratella, the one that I normally see -- S. serratoides -- is very distinct in terms of the sternites: there is "a transverse row of four black dots on each sternite." (Beaty, p. 31)  These.

Now look at the sternites on the nymphs from this morning.

Totally different.  So, I think we have a new species: Serratella carolina.  However, I will continue to examine this further.

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One other mystery bug at the Doyles -- a common netspinner, genus Ceratopsyche.

I found two of these larvae and picked them up because of the color -- cream colored bodies with brown nota and heads.  I also found a Ceratopsyche bronta and a Ceratopsyche morosa.  Those I could identify -- this one, so far, I cannot.  What is critical in making this kind of ID is the pattern we find on the head, and I've not seen this one before.

Three, dark horizontal lines in the posterior angle of the frontoclypeus.  I've asked Steven Beaty for help and will get back to you when he responds.
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Other photos:

1. Oh yes, I did find some small minnow mayflies at the Doyles: Baetis intercalaris, every nymph that I saw.

2. And as promised, here's the Leucrocuta flatheaded mayfly I found at Buck Mt. Creek.  A beauty!

Correction: That's a female Plauditus dubius, not Iswaeon anoka

Sorry.  This is not I. anoka -- it's a female Plauditus dubius.  I was thrown off by its size.  As I noted this nymph is close to 5 mm; P. dubius nymphs tend to be smaller -- 3.0 - 3.5 mm.  But two things are off: 1) the median caudal filament on I. anoka is longer than segment 10: it looks like this.

That is not true for the nymph that I found today.  And 2) as noted in Beaty's description, there are "midventral dark spots ...present on abdominal sterna 2-8 or 9."  These.

There are no such marks on the nymph that I found today.  I can also note that the widening of the tibia from the base is more distinct on I. anoka than what we see on P. dubius.  It should look like this:

This is Iswaeon anoka, for which I will look in the Rivanna as soon as it clears.

Second sighting of the "uncommon" small minnow mayfly "Iswaeon anoka": a new stretch of South River

(Note: See the next entry.  This identification was wrong.)

I was hoping to find some small minnow mayflies today -- and I did -- but I didn't expect to see this one.  Iswaeon anoka.   I've seen this species only one time before -- at the Rivanna River on 6/24/12 (see the posting on 6/25).  Today I went to South River up in Greene county, but I was wading 4-5 miles downstream from the site in the mountains to which I normally go.

Beaty notes, on the genus Iswaeon, that it's "primarily a mountain taxon, usually collected in the summer": I. anoka, he adds, is "uncommon." (Beaty, "The Ephemeroptera of North Carolina," p. 10)
Let's review (citing Beaty's description):

I. anoka -- nymphs ~ 4 mm; a small, sometimes indistinct, dark dot at each tibial-femoral junction; large, a distinct dark spot laterally above the meso-and metanotal coxae; large median dark spots sometimes present on terga 2 and 6; midventral dark spots sometimes present on abdominal sterna 2-8 or 9; dorsum of abdomen often with a pale median longitudinal stripe set against a darker background, sometimes reduced to small pale spots and interrupted on middle segments; caudal filaments with dark medial band.

I should add that the defining feature of the genus Iswaeon is: "tibia narrow at base and distinctly widened medially to apically."  That we can see in the photo below.

Also clear in this photo is the small dot at the "tibial-femoral connection."   In this next photo, we can see the dark dots at the meso- and metanotal coxae.

The "large median dark spots" on terga 2 and 6 are clear on 2 on this nymph; it's a bit of a stretch to see one on 6.  That we can see in this photo on which I've also noted the pale median longitudinal stripe.

Here's a good look at the dark medial band on the tails (caudal filaments).

Very cool.  I'm so glad to find this one again.  I've been planning to look for it in the Rivanna, but the Rivanna is high and muddy, and likely to stay so for sometime to come.

This nymph was close to 5 mm.
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The other small minnow mayflies this morning?  One tiny Baetis intercalaris, probably the most common small minnow we see in the summer, and a couple of Acentrella turbidas.

B. intercalaris:

A. turbida -- a real beauty:

And a second A. turbida alongside the I. anoka:

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And I found quite a few Drunella cornutella spiny crawlers.  I guess there a lot more common than I had assumed.

Perlesta common stoneflies galore!

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And here are the riffles in which I was looking.  Pretty spot: I'll be back.