A "hat-trick" on Flatheaded Mayflies at the Doyles: E. pleuralis, E. vitreus, and Rhithrogena

And all three species in the same set of riffles!  Number 1: genus Rhithrogena -- three tails and fan-like gills that form a complete oval on the ventral side of the abdomen.

Number 2: Epeorus pleuralis -- two tails with fan-like gills that do not connect on the ventral side of the abdomen; tracheation in the gills is barely visible.

And number 3: Epeorus vitreus -- two tails with large, fan-like gills in which the tracheation is very pronounced.

The rocks were covered with flatheads: most numerous  -- the Rhithrogenas.  This was one of the few places I've visited in recent weeks where spiny crawlers were outnumbered by some other insect.  Another view of the three.

Tolerance values: Rhithrogena -- 0.0; E. pleuralis -- 1.5; E. vitreus -- 1.2.  Pretty good water in the Doyles River at Doylesville.
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I was surprised to see all three flatheaded species together.  But there were other surprises in store.  Like this common stonefly.

This one is genus Perlesta, and if you look back to blog entries for last June and July, it will be clear that  we normally see Perlestas in early summer -- not in late April, at least not any that are already looking fairly mature (note the shape of the wing pads)!  The features we use to ID this species are the wavy, incomplete row of spinules on the occipital ridge and the branched subanal gills.

The other "surprise" was something I've not seen before: a fully mature Nemourid stonefly, genus Amphinemura, one with black wing pads.  Sorry for the poor definition -- this is a very small insect (around 5 mm).

Pretty cool.

Of course, there were spiny crawlers, and they were E. dorothea.  Orange and brown seem to be common colors.

Below: an I. holochlora Perlodid stonefly sees its reflection in the petri dish.

Oh.  And I was hoping to find some small minnow mayflies -- and I did, but by then it was too overcast to get a good photo:  Baetis intercalaris.

Cinygmula subaequalis: Back to the South River

It was sort of "the day of the flathead" up at South River: the bottoms of rocks were covered with Epeorus pleuralis, Epeorus vitreus, and this little beauty, Cinygmula subaequalis.  To date, this is still the only place where I've seen Cinygmula nymphs.  This is a genus you can pick out with a good loupe by looking down at the head.  The maxillary palps are visible at the sides of the head, as is the fact that the front of the head is emarginate.

This is a species we only find in high quality streams: tolerance value, 0.0.  And I can attest that they are hatching.  On one of the nymphs I picked up, the wing pads had already separated and lifted up from the body revealing the adult wings underneath ready to unfurl.

The Epeorus vitreus nymphs that I found were very large, and they were brown:  the E. vitreus nymphs that I'm used to seeing are a greenish yellow.

Remember that we can pick out this species by the four, irregular shaped spots at the front of the head. (Please click to enlarge.)

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I found a real mix of insects today, though here, as elsewhere, there were more spiny crawlers than anything else.  To my surprise there were still a lot of Isoperla namata Perlodids: in Albemarle county they've become pretty scarce.  Some photos.

1. Common netspinner larva: Diplectrona modesta (the species we only find in good streams).

and with a spiny crawler

2. Two very colorful and elaborately patterned spiny crawlers, both E. dorothea.

3. A Nemourid stonefly, genus Amphinemura -- with wing pads that are starting to flare away from the body.  Note the "cervical" gills sticking out from the neck (bright white).

4. And one of many Isoperla holochlora nymphs that I saw, one that's much less mature than those I found on Tuesday at Powells Creek in Crozet.

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The Spiny Crawler "Eurylophella verisimilis"

I noted on Tuesday that I was hoping to ID the Eurylophella spiny crawlers that I've been finding to the level of species: it turned out to be pretty straight forward.  All of the Eurylophellas that I've found so far are Eurylophella verisimilis, which, it turns out, is "the most common Eurylophella in the Piedmont and Mountains" (Beaty, "The Ephemeroptera of North Carolina," p. 29).

E. verisimilis belongs to the E. bicolor group (Beaty, p. 28) on which the "submedian tubercles on terga 1-4 [are] relatively short, stout and blunt."  (I couldn't get a good photo of that.)  On the species ID, Beaty says the following:

E. verisimilis -- nymphs 6.8-9.2 mm; this is the only species in the bicolor group with well-developed occipital tubercles; the dorsal tubercles are dark on segments 5-7 (between gills).


Both of those features are easy to see.  (My largest nymphs were 7-8 mm.)

Occipital tubercles:

Dark tubercles on segments 5-7:

The large gills on segment 4 -- operculate gills -- cover and protect the delicate gills on segments 5-7.
This is a nymph that is somewhat tolerant of siltation (TV = 3.9), so the gills must be protected.   Three of the four E. verisimilis nymphs that I've found have been pretty well covered with sand and mud.

This nymph was the one that I found at Powells Creek on Tuesday (4/24).

And I found this one in a small stream in Sugar Hollow on 3/21/11.  (Note the dirt!)

And the most mature specimen that I've seen is this one: Buck Mt. Creek, 6/3/11 (also pictured in the photo at the top of the page.)

詢 (or 訪) 不遇 ("Looking for..but not finding"): a Trip to the Powells

A number of Tang dynasty (roughly 600-900 AD) poets wrote on a theme called xun (or fang) bu yu 詢 (or 訪) 不遇 -- "looking for X (often the name of a recluse) but not finding him home."  I'm often reminded of those poems when I make my trips to the streams.  Today I went to Powells Creek in Crozet where I was "looking for" -- and expecting to see -- various small minnow mayflies and genus Neoperla common stoneflies.  Neither was "home"!  But I did find things that I wasn't expecting to encounter.

Above, a pretty mature common stonefly, Eccoptura xanthenses.  Beautiful colors, fully shaped/arced wing pads, and note how tergites 8-10 have turned black.  Like the Acroneuria abnormis that we saw last week, this common stonefly will be hatching in June or July.

I wasn't really surprised to see E. xanthenses: this is a species I usually see when I come to this stream.  But I did have three surprises.

1. I found two, fully mature Diploperla duplicata Perlodid stoneflies.  This is the largest of the two (11-12 mm).

This is a nymph we've been seeing all winter and spring -- and I've seen a lot of them lately in a number of streams.  All in all, it's a pretty drab insect compared with the many spectacular Perlodid stoneflies we find.  But, when they mature, they exhibit very rich colors and patterns.

2. Surprise number 2: Among the millions (well, a bit of an exaggeration!) of spiny crawlers on the leaves and the rocks-- they all appeared to be E. dorotheas -- was one spiny that we don't see all that often -- genus Eurylophella.

This is the type of spiny that has a large gill on tergite 4 that essentially blocks the gills on 5-7 from view.

I think this is only the fourth Eurylophella I've seen since I started taking pictures of aquatic insects, so I've not yet worked on identifying these spinys to the level of species.  Work to do on a rainy day.

3. And surprise number 3: Coming in second to the spiny crawler today in terms of sheer numbers -- the Perlodid stonefly Isoperla holochlora.

True, I'm seeing them now in a lot of the streams I explore, but I picked up 20-30 nymphs today (all returned to the stream) without looking real hard.  And, note that in Powells Creek, the I. holochloras have begun to mature.  Note how the rear wing pads are starting to flare out from the body.

Small minnow mayflies and Neoperla Perlids?  Just have to find them next time!

Drunella tuberculata: Making the Case

On 4/17 I posted this photo -- and the one that follows -- of two genus Drunella spiny crawler nymphs that I found at Buck Mt. Creek.

I noted that although the two nymphs differed in color -- note the banding on the legs of the insect in the first photo -- anatomically, they were exactly the same: both have occipital tubercles, both have a single tubercle on the mesothorax, and both have prominent tubercles on tergites 5-7.  On this side view of one of the nymphs, you can clearly see the occipital tubercles and the methathoracic tubercle: we'll see the abdominal tubercles in a later photo.

While I was undecided on 4/17 whether these nymphs were D. allegheniensis or D. tuberculata (citing Beaty's descriptions), I did additional work on this issue over the weekend, and I think I can now prove that both nymphs are Drunella tuberculata.  Let me do this first, using the evidence Beaty provides ("The Ephemeroptera of North Carolina," p. 25), then add additional support from an article by Luke M. Jacobus and W. P. McCafferty ("Revisionary contributions to the genus Drunella," pp. 127-147 in the Journal of the New York Entomological Society, Vol. 112, No. 2/3, 2004.)  This article is available on line at: http://findarticles.com/p/articles/mi_6920/is_2-3_112/ai_n28247003/?tag=content;col1.)

Using Beaty's descriptions, there are two things we have to decide: 1) is there a "dark transverse band" across the frons (face), and 2) do the occipital tubercles "diverge"?  If the answer to both of these questions is "yes," then our nymphs are D. allegheniensis; if the answers are "no," then they're D. tuberculata.  Let's look at the faces.  First, the "brown" nymph, the one without leg banding.

Nothing I would call a dark transverse band.  And here is the face of the nymph with the banding.

No banding.  (Note: what appears to be a dark line between the eyes is actually a "seam" that appears darker in the photo than it actually is.  In any event, it is posterior to what is normally considered the frons.)

Do the occipital tubercles "diverge" apically.  To the contrary, I'd say that they "converge."  Have a look.

So, using Beaty, I'd have to go with D. tuberculata.  But the features on which Jacobus and McCafferty focus is even more convincing.  For me what is critical is what they say about the denticles (teeth) on the tarsal claws and the setae (hair) on the terga.

D. tuberculata: "The claws usually have five or fewer denticles."

D. allegheniensis: "...usually has more claw denticles than sympatric congeners [like D. tuberculata], and in D. allegheniensis, these denticles are situated along most of the length of the claw, rather than basally only."

I can only see three denticles on the claws, and they are "basal only."  Picture.

D. tuberculata: "Long, hairlike setae protrude dorsally on abdominal terga 8 and 9."

D. allegheniensis: "Drunella allegheniensis does not have long setae that protrude dorsally from the hind margins of abdominal terga 8 and 9."  Have a look at the terga of one of our nymphs.

I think that's pretty convincing.  Drunella tuberculata.

Let me note in conclusion that Donald Chandler has posted a photo on Discover Life (http://www.discoverlife.org/mp/20p?see=I_DSC427&res=640) of a Drunella tuberculata nymph, and it looks exactly like these.