A real mix at the Rapidan River today -- but a beautiful Stenacron interpunctatum

It's the flatheaded mayfly that I don't see all that often: today it's the first insect I saw.  The fleatheaded mayfly, Stenacron interpunctatum.  On the bottom of a rock-- like almost all flatheaded mayflies -- close to shore.  The Rapidan's still fast and high, so I had to stick to the edge of the current.

This type of flathead is easy to spot because the body is long and thin.  Beaty describes this species this way: "nymphs 8-11 mm; 7-10 spines on maxillary crown; white streaks, often in H-pattern on tergites 8-9; caudal filaments with alternating banding pattern.  A spring and summer species.  The most common and tolerant Stenacron species in NC" ("The Ephemeroptera of North Carolina," p. 22). This nymph was 10 mm.  The white streaks on the abdomen are obvious.  We can see the "banding" on the caudal filaments (tails) by looking closer as well as shallow "H" on tergite 9.

I wish this nymph had kept all 6 of its legs, but if you look twice at a flathead, it sheds legs and gills!

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On the very same rock, I found one of the things I was expecting to see -- the cased caddis, Pycnopsyche scabripennis.

The Rapidan always has them at this time of year, and this case construction is common -- kind of resembles a hot dog that's covered with ketchup and relish.  These are big larvae.  This one was 22 mm, the case just a little bit longer.  I found three of these larvae this morning, all with the very same case, though one had added a long stick to one side as an extension.

But there were other case-makers around.  I also found the humpless casemaker, Brachycentrus appalachia, and the strong casemaker, Psilotreta labida.  I was expecting to see lots of B. appalachia larvae -- but I only found one, and it was still very small.

And at long last, I'm starting to see some of our "summer" small minnow mayflies.  Today it was Baetis pluto (female)...

and Baetis intercalaris (male), the one with the parentheses marks -- ( ) -- on the terga.

The B. pluto nymph was fully mature -- ready to pop -- as we can see from the dark color and the black wing pads.  Normally, tergite 5 is very pale compared to the rest.  But there are other features that give it away, such as the dark, medial banding on the caudal filaments (tails), and the length of the middle tail ("3-4 to subequal to lateral filaments").  (See Beaty, "The Ephemeroptera of North Carolina," p. 6)

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Still tough to find good streams to explore.  I count on the Rapidan and the Rivanna for interesting insects in the summer.  The Rivanna remains unwadeable, so I may be heading to Madison county a lot.

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Oh.  A Perlesta "common stonefly," of course.

A nice find at Buck Mt. Creek: the Green Stonefly, Alloperla

I wasn't sure what I'd find this morning at Buck Mt. Creek.   Surely the flatheaded mayflies, Epeorus vitreus, and maybe some small, small minnow mayflies since we've moved into the hot, humid weather of summer:  I found both.  But the find of the day was this maturing green stonefly (Chloroperlidae), genus Alloperla.   I've seen them before, but only a couple of times.

Let's look at Beaty's description.  "Genus Diagnosis: Nymphs ?? mm; pronotum with setae usually restricted to corners; mesal portion of posterior margin of abdominal sternite eight lacking setae; distal end of cerci with feather-like surface (in lateral view) due to 2-6 long setae between apical coronas."  "Primarily found in gravel and riffle areas of small to medium streams..."  "Mainly collected January through May in the Mountains.  Uncommon."  ("The Plecoptera of North Carolina," p. 9)

He adds: "North Carolina has at least seven species of Alloperla of which the nymphs of most of these species are undescribed (including A. lenati).  So we leave the description at the level of genus.

1. This is a very small stonefly: this one measured a mere 6 mm.

2. Despite the small size, I was able to see the setae at the pronotal corners.

3. I could not get a good photo of the 8th sternite.

4. On the "feathery" tips of the cerci (tails), this is the best I could do, but you can see the long setae "between the apical coronas".

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Pretty special.  Always nice to find something "uncommon," and given the small size of this nymph, I was pleased with my photos.

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The other stonefly I found is one that we commonly see at this time of year: the "common" stonefly (Perlidae), genus Perlesta.  Found two.

I don't know if I've called this our "June" Perlid before, but the name is certainly fitting.  It's a univoltine Perlid, meaning there's a single generation each year, and we see them from May to July.   Like the Alloperla I found, this Perlid cannot be ID'd to the level of species.  However, Beaty does say that some species are "currently being associated" ("The Plecoptera of North Carolina, p. 19), so I might check in with him to see if any progress has been made in that direction.

Genus Diagnosis: Nymphs 8-12 mm; setal row on occiput complete, sinuate, and with irregular gaps; abdomen with numerous short, stout intercalary setae, often with pigmented bases giving abdomen a speckled appearance; anal gills present; body covered with fine, dark clothing hairs. (p. 19)

setal row:

abdomen:

It's a no brainer: they're genus Perlesta.

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But I did find Epeorus vitreus, and I did find some small minnow mayflies including the first Acentrella nadineae of the season.  We'll see plenty of them throughout the summer.

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Chloroperlid, genus Alloperla.

(For a full discussion of the features used to ID Alloperla, see the entry posted on 5/26/12.)

The flatheads of summer: Entry Run and South River

We've reached the time of year when I like to get out of the small mountain streams: my focus turns to the summer small minnow mayflies which tend to inhabit larger streams, being more tolerant of warmer waters.  But, we're still waiting for those streams and rivers to clear.

So, my Father's Day present was a trip up to Greene county to explore Entry Run and South River.  What I found was no big surprise -- lots of flatheaded mayflies on the bottoms of rocks: Leucrocutas, Epeorus Vitreus, and Epeorus fragilis.

In the photo at the top of the page, the common Epeorus we find in the summer, E. vitreus.  We often find it in the very same streams in which, in the winter and spring, we find Epeorus pleuralis.  To ID these nymphs, all you have to do is look at the front edge of the head: "Head with distinctive color pattern of four irregular pale spots on anterior margin."  (Beaty, "The Ephemeroptera of North Carolina," p. 17.)  Easy to see.

And the other flathead that's common at this time of year in our clean mountain streams -- usually in the smallest of streams -- is Leucrocuta.  I saw a lot of them today.  Leucrocutas are tiny (6-8 mm) and hard to pick up and keep them intact.  But I managed to get some good photos today.

If you follow this blog in a regular way, you know that Beaty urges us to keep Leucrocuta ID at the level of genus.  Still, there are two sources that would call label the nymphs that I found today Leucrocuta hebe.  (See Knopp and Cormier, Mayflies, p. 152, and the photos posted by Chandler:
http://www.discoverlife.org/mp/20q?search=Leucrocuta+hebe.)   The key feature -- the pale "U-shaped" spots on several abdominal terga.

I also saw at least one Epeorus fragilis -- but I didn't get a very good photo.

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Just a few other things.

1. There and fewer and fewer E. dorothea spiny crawlers around as most have hatched as Pale Evening Duns.  But I did snap some shots of a male and a female.

2. Another left over from spring: Perlodid stonefly, Isoperla holochlora.

3. And one of the common netspinners that are quite "common" during the summer, Ceratopsyche slossonae.

While the head appears to be totally dark brown/black, there's actually a pale yellow spot right in the middle.

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Back to the ID of those pesky Maccaffertium flatheads from Buck Mt. Creek and the Doyles

Back from Europe -- and back to streams that are high and off color.  Ugh!  Still, I also came back to some help from Steven Beaty with the species ID of the Maccaffertium flatheaded mayflies that I found at Buck Mt. Creek on 5/15 -- in the picture above -- and at the upper Doyles River on 5/24.  (I had sent him the nymphs in a vial.)

On this nymph from Buck Mt. Creek -- with the pronounced banding on the femora -- according to Beaty, it is probably M. modestum.  This was determined by slide mounting the mouth parts and the tarsal claws and noting the ventral pattern.  That means there are "more than 30 hairs and 2-3 spine-like setae on [the] maxillary crown," and that the protarsal claws lack denticles." ("The Ephemeroptera of North Carolina," vers. 2, p. 35)

While I can visually ID M. vicarium, M. merririvulanum, and M. pudicum by noting their dorsal and ventral patterns, M. modestum cannot be ID'd in that way ("highly variable dorsal and ventral patterns," Beaty, p. 35).  Beaty notes "two common ventral patterns" for M. modestum, but our nymph has no pattern at all.

What we can see in this view of the venter is that on M. modestum nymphs "posterolateral projections [are] absent anterior to segment 6" (p. 35).

By the way, Donald Chandler has posted photos of M. modestum on Discover Life, and his nymph looks a whole lot like mine.  (See: http://www.discoverlife.org/mp/20q?search=Maccaffertium+modestum.)
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And what about this nymph that I found in the Doyles River on 5/25?

My initial conclusion was right: it's M. ithaca, a species we commonly see at this time of year (the "Light Cahill" for you fly fishermen).   Again, Beaty mounted the mouth parts and the protarsal claws and took a close look at the venter.   On M. ithaca nymphs there are "15-35 (usually 20-30) hairs and 4-6 spine-like setae on [the] maxillary crown."  ("The Ephemeroptera of North Carolina," p. 34)  I could see 5 spine-like setae on the crown with my microscope; I was not able to count the hairs.  I could also see with my microscope a denticle (tooth) on the protarsal claws.

Beaty says that M. ithaca claws usually lack denticles (p. 34), but in an email he sent me two years ago, he noted that they may or may not have denticles.  Clearly, our nymph had them.

As I had noted on 5/24, the ventral pattern we find on our nymph closely resembles that of M. mediopunctatum -- but it's not exactly the same.  Here's what we have on our nymph:

 While M. ithaca and M. mediopunctatum both have an inverted "U" on segment 9, the "sternal maculations" on segments 3-8 (the cross bars) are curved on M. ithaca; they're fairly straight across on M. mediopunctatum, and they're flush with the anterior edges of the segments.  (See: http://www.troutnut.com/specimen/574.)

So there you go.  Nothing "exotic" or new.  But once again we see the need for close-up microscope work to be sure of species ID.
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And less than one week ago I was enjoying my lunch in Amsterdam by this lovely canal!