The end of one season, the start of another: Baetis flavistriga and Baetis tricaudatus up at South River

For awhile I saw nothing but stoneflies -- Giants and Commons -- at the South River (Greene County) this morning.  But then I picked up this little critter which I knew was a small minnow mayfly, so I paused to take photos.

What a beauty!  The small minnow mayfly Baetis flavistriga.  I've found them before, but I've never seen one with these spectacular colors.  Beaty says this one can be found in our streams from April through November ("The Ephemeroptera of North Carolina," p. 6) and that it's "common," but I've actually seen very few.  They're small: the range is 4-6 mm.  This one was about 4.5 mm; this photo gives a better impression of its actual size.

While we should look at the labial palps to be certain of our ID, there are two physical features that will suffice: 1) there are "two large submedian kidney shaped spots" on the abdominal terga," and the "caudal filaments [have] a medial dark band."  (Beaty, p. 6)

I also found a mature Acentrella nadineae, another "hanger-on" from the summer.

But there was also a sign that we're moving into the winter when we see a different set of small minnow mayflies.  I found the first Baetis tricaudatus of the season.  Note the length of the tails (caudal filaments).  With this species the "middle caudal filament [is] less than half as long as [the] lateral filaments."  (Beaty, p. 6)

True, at this size -- 3.5 mm -- they're not much to look at.  But this is what we'll be seeing in South River in February and March when they'll measure from 5 to 8 mm.

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Of caddisflies, I found common netspinners (C. alhedra), fingernets (Dolophilodes), and a number of small freeliving larvae.  In this stream, all of the freeliving larvae seem to be Rhyacophila fuscula, the green one with the "topless" H pattern on its head.

But the caddisfly find of the day was this "Saddle-case maker," Glossosoma nigrior.

I have never seen a Glossosomatid make that kind of case.  Their cases are invariably "dome-shaped." Obviously this little larva forgot to look at the blueprint!  That white pebble on the left side was not a very good choice.   As Glossosomatids commonly do, this larva eventually crawled out of its case.

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Of course we mustn't leave out all of those stoneflies.

1. Common stonefly, Acroneuria abnormis.

2. Common stonefly, Paragnetina immarginata.

3. Giant stonefly, Pteronarcys proteus.

4. And Giant stonefly, Pteronarcys biloba.

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But this one, for me, made the day: small minnow mayfly, Baetis flavistriga.

The Rivanna flatheaded mayfly of the moment: Maccaffertium modestum

When I went to the Rivanna River at Crofton last week I found a flatheaded mayfly that looked much the same as the one in the photo above, but I failed to get any useable photos.  So yesterday, I went to the Rivanna at Darden Towe Park to see if I could find the same insect -- and I did.  What's the species?  It appears to be Maccaffertium modestum, which, says Steven Beaty, is the "most common [Maccaffertium] species in North Carolina."  ("The Ephemeroptera of North Carolina," p. 20)

That probably means that it's common in Virginia as well and that I've seen it before, but I've been hesitant to attempt this species ID.   I'll tell you why.  Let's look at Beaty's description.

M. modestum -- nymphs 8-11 mm; has 15-50 (usually 20-40) hairs, 4-7 spine-like setae on maxillary crown; claws with denticles (some specimens have one foreclaw with and the other foreclaw without denticles) highly variable dorsal and ventral color patterns.

Now, that's not a whole lot to go on for the "most common" species we see.   First of all, as I've shown in previous entries, it is not easy to count the hairs and the spines on the maxillary crown of a Mac, especially when the nymph is a small one, and while I can usually see if there are denticles on the foreclaws, that trait does little to narrow down the possible species ID.  That leaves us with a "highly variable dorsal and ventral color pattern."  I.e. it leaves us with nothing to go on.

However, this description has been expanded in the second version of Beaty's Ephemeroptera manual.  (Go to: http://portal.ncdenr.org/web/wq/taxonmanual).   Much improved.

modestum -- nymphs 8-11 mm; has 15-50 (usually 20-40) hairs, 4-7 spine-like setae on maxillary crown; claws with denticles (some specimens may have one protarsal claw with and the other without denticles); posterolateral projections absent anterior to segment 6; highly variable dorsal and ventral color patterns; two common ventral patterns: (1) presence of anteromedial bars on 7-9 with bar on 7 possibly obscure and that on 9 extended posterolaterally to form an inverted "U" or (2) sterna 2-8 with two pair of small dots; one pair anteromedially placed and the second pair posterior and lateral to the first pair; may be faint on anterior segments.

Is this a good description of the nymph that I found yesterday?

1) maxillary crown

While this is not the best of photos, I have no trouble seeing at least 15 hairs on the crown, and through the microscope, I could count 6-7 spine-like setae.

2) denticles are present on the tarsal claws

3) posterolateral projections

They are very clear on segments 7-9 -- that's about it.  Certainly nothing there before segment 6.

4) So we're back to the issue of ventral pattern.

Pattern 1, I'd say, is out: there are no bars on sterna 7-9.  Pattern 2?  Possibly.  Two pairs of medial dots are clearly visible on segment 6, though the posterior pair does not appear to be "lateral" to the anterior pair.

So, can we call our nymph M. modestum?  I think we can, but we need to turn once again to Don Chandler's photos posted on "Discover Life."  (Go to: http://pick4.pick.uga.edu/mp/20q?search=Maccaffertium&flags=glean:&mobile=close)  I think his photos of M. modestum -- both dorsal and ventral -- confirm this ID.  We just need to add this to Beaty's description.

Maccaffertium modestum

By the way, this is the most tolerant Maccaffertium species we find, with a TV of 5.7.
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As I did when I explored the Rivanna at Crofton, I found lots of stoneflies at Darden Towe, including the very same A. abnormis -- the one that lacks the "M" pattern on the head and has an abdomen that's entirely brown.  It's a big nymph.  This one -- still immature -- measured 13 mm.

And as we can see in this second photo, Agnetina annulipes was also present.  Note the difference in species size: A. annulipes is small.

Finally, I again saw quite a few Giant stoneflies, Pteronarcys dorsata.

Stonefly day at the Rivanna: Giants and Perlids, including Agnetina Annulipes

Another day when persistence was rewarded.  I've been trying all summer to reach some riffles in the Rivanna at Crofton where I've found good things in the past: today I finally got there.  And I found at least one of the insects I was hoping to see: this is the Common stonefly (Perlid) Agnetina annulipes, a nymph that, so far, I've not seen anywhere else.   I picked up quite a few in the tangled river weed on the tops of the rocks, but they're easy to miss since they're very small nymphs.  The largest I found was this one

which was a mere 9 mm.  Clearly, these nymphs are not yet mature -- the posterior edge of the wing pads is just starting to bend -- still, I don't think this species gets very big.

Let's review the species ID.  "A. annulipes -- nymphs ?? mm; head pattern roughly M-shaped with arms directed posterolaterally, some specimens may have an almost interrupted mask; dorsum of abdomen banded, with dark bands on anterior half of segment, sometimes segments 5 and 6 dark mostly to posterior margin; tergum 10 mostly dark including the apex.  Semivoltine.  Collected from the Mountains and Slate Belt.  Also recorded from SC and VA."  (Beaty, "The Plecoptera of North Carolina," p. 15)

For the genus ID, Beaty notes "Occiput with setal row or ridge complete...anal gills present."  Let's look at our nymph.

Perfect, but I'd say that the posterior extension of the dark band on tergite 6 is clearer than that on 5.

North Carolina does not assign a tolerance value to A. annulipes, suggesting that it is not often seen.

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The other Perlid I commonly see in the Rivanna is our "common" species Acroneuria abnormis, and I found some today.  But the nymphs that I see in this river often differ from those I see everywhere else.

Let's look again at Beaty's description of A. abnormis.  "...dorsum of head with a well defined M-shaped head pattern, sometimes with interruptions; posterior margins of abdominal tergites light, dark tergal bands irregular; or dorsum of head without M-shaped head pattern and abdomen uniformly brown."  (Beaty, "The Plecoptera of North Carolina," p. 14)

Almost all A. abnormis stoneflies I see do have the "well defined M-shaped head pattern," and tergites on which the posterior margins are light.    They look like this

or like this.

(Look again at the entry posted just six days ago on 9/13.)  The  A. abnormis nymphs I see in the Rivanna are clearly the "or" version that Beaty notes:  "dorsum of head without M-shaped head pattern and abdomen uniformly brown."

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One other odd stonefly today.

Very strange!  It's a Giant, of course, and it's clearly Pteronarcys dorsata, and I saw a lot of those nymphs today.  But this is what the others all looked like.

Note again the P. dorsata key features: no lateral projections on the abdominal segments with very pronounced, "produced" angles on the pronotum -- they're very pointed on this one.   So what is this strange looking critter?

It took me awhile to figure it out, but clearly it's a P. dorsata nymph that has just recently molted.  Nothing has darkened.  The antennae are white, the cerci and legs are still white, and the body's light brown.  Very cool!
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Agnetina annulipes

Odontocerids (Strong case-makers) at the Rapidan River

With very little to see in our local streams at the moment, I decided to return to the Rapidan River where I knew I could find lots of insects.  One of my goals was to find some Odontocerids -- Strong case-maker caddisflies -- for photos, and it wasn't much of a problem.  When I walked into the stream, I looked down at some submerged rocks in the slow water -- and there they were.  They graze on the algae and periphyton on the tops of the rocks, so you don't have to lift a thing to see them.

Strong case-makers -- at least the genus we commonly see, Psilotreta -- hatch as "Dark blue sedges" in late spring/early summer, but the time to see them in their beautiful cases is now.    Ames (Caddisflies, p. 211) says that he sees them in New England in the fall, from August through October.  Some make tubular cases; others have cases that are long, tapered and curved.  I found both types of cases this morning, but I forgot to photograph the plain, tubular case.

Look for them in clean mountain streams.  I see them every year in the Rapidan, the North Fork of the Moormans, and South River up in Green county.  The most common species we see is Psilotreta labida.
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Other photos:

1. Small minnow mayflies, Acentrella nadineae.  I also saw Baetis intercalaris nymphs, but somehow I managed to break their tails.

and this one decided to perch on this humpless case-maker case

2. And yes, as I expected, I again saw a lot of humpless casemakers -- Brachycentrus appalachia.

If you look closely at the head of this larva, you can make out the 5 black stripes that help us to key out the species to B. appalachia.

3.  I saw quite a few fingernet caddis larvae this morning, genus Dolophilodes.  Note the assymetrical notch on the leading edge of the head.

4. And you guessed it, that's a small roach-like stonefly alongside our larva.  There were lots of them in the leaf packs.  They're tiny at this time of year.

5. One of those young common stoneflies I've been talking about.  This one is Paragnetina immarginata.

6. And I found both Giant stoneflies that inhabit this river: Pteronarcys proteus and Pteronarcys biloba.  The lateral projections on the abdominal segments differ dramatically on the two as we can see in these photos.

P. proteus

P. biloba

P. biloba cerci (tails) are quite a bit longer than those of P. proteus.