Two really stunning insects today: Paraleptophlebia guttata and Leucrocuta hebe

Really gorgeous: a fully mature flatheaded mayfly, Leucrocuta hebe.  Location: Doyles River up at Blackwells Hollow Road.   Some more photos and then we'll go into the species ID.

At 4 mm, this was a very small nymph.  Still, the photos worked out just fine.  On the species ID -- in the past I've called this one Leucrocuta hebe using a number of sources.  But today I turned to our new key to see what I'd find.   This key seems to urge more caution with making this call, but all in all I think we're right with L. hebe.  New key ---

"L. aphrodite and L. hebe may have a pale medial V-shaped area on abdominal terga 7, 8, and most of the medial length of 9, or on tergum 9, three connected or unconnected pale spots (possibly even one medial spot in extreme variants).  Sternal and caudal filament markings that have been associated with either of these species vary considerably between and among populations, and other characteristics that may be of diagnostic value are not known with confidence.  For example, L. hebe might have an unmarked ventral abdomen or one with pairs of ventral spots in some populations, and also commonly a pair of posterolateral spots on sternum 9, or extensive lateral staining on 9." (Larvae of the Southeastern USA: Mayfly, Stonefly, and Caddisfly Species, p. 110)

What I see on our nymph is this.  1) There is clearly a "V" (or a "U") on tergum 7, 8 is pretty solid in color medially, and on 9, I'd say there are 3 pale unconnected spots.

This is the venter.

The ventral abdomen on our nymph is "unmarked" while on segment 9, there is, I think, lateral staining.  I think L. hebe is the right call.
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Nymph number two -- a fully mature pronggilled mayfly, Paraleptophlebia guttata.

I wasn't sure of the species ID on this little guy (also 4 mm) -- the pale terga were a little unexpected -- so I decided to key it out.  P. guttata for sure.  1) "Gills 2-7 forked near base, usually not more than one-sixth length from base; gill trachea without distinctly pigmented lateral branches."  (Larvae of the Southeastern USA, p. 140).

2) "Combined length of distal two maxillary palp segments about 1.5x or more length of proximal segment." (p. 140)  Segments 2 and 3 were 1.6 times as long as segment 1.

3) "Posterolateral projections present on abdominal segment 9 only." (p. 140)  Yes.

and 4) "Abdominal terga 2-6 laterally without blackish bands (as on P. strigula), but often with diffuse blackish spot in posterolateral corners." (p. 141) Yep, those spots are there.

 Paraleptophlebia guttata.
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Beautiful day in Virginia.  Stream level was great.  But now we're on the lookout for Hurricane Irma!

Another brushlegged nymph from Buck Mt. Creek: see no reason to doubt the ID -- Isonychia georgiae

I took photos of two of these nymphs yesterday: this is the second.  The morphology this time really confirms, I think, the ID of Isonychia georgiae.

"Filamentous forecoxal gills each with single filament."

Yes.  "Abdominal sterna with markings similar to any of Figs. 2.386-2.389."  Figure 2.388 looks something like this.  (.°.)  In the middle of the sterna there are what look like parentheses marks.  Above and between those marks there is a small pale circle, while in-between those marks at the bottom there are two smaller pale dots.  Have a look at sterna 6-8 on our nymph.

Bingo!  That pattern's as clear as can be, especially on sterna 6.

Finally, "Abdominal sterna 6-8 with markings similar to any of Figs. 2.386-2.388; abdominal terga yellowish brown to dark reddish brown (with or without lighter mid-longitudinal stripe)...... Isonychia georgiae."  As we've seen, we have an exact match for pattern 2.388.  I'd say the terga are dark reddish brown.

One other thing I might mention, that the gills are rosy/purplish in color is apparently also used in diagnostics.  (See the comment by Roger Rohrbeck at http://bugguide.net/node/view/1387557.)

Exploring species ID for Brushleggged mayflies (Isonychiidae)

Brushlegged mayfly nymphs are fairly easy to find -- if not prolific -- in many of the streams that I visit: the Rivanna River, Buck Mt. Creek, the Rapidan River, and so on.  I've taken photos of many of them over the years but no longer bother since they all look the same and species ID isn't encouraged.  Leave them at genus: Isonychia.

But emboldened by the species descriptions in our new key (Larvae of the Southeastern USA: Mayfly, Stonefly, and Caddisfly Species, pp. 126-129), I've decided to look more closely at what I'm finding this year.  All the same species?  Species that vary by stream?  Can I decide on the species with any exactness?  That's why I was excited this morning to find this nymph at Buck Mt. Creek.  It looks nothing like the brushlegged nymphs that I commonly see, which look like this.

Clearly visible here is a wide, pale stripe that runs from the head to the tails.  Nothing like that on the nymph that I found today.

Intriguing.  Let's see what we can find out from our key.  Couplet one.

239  Filamentous forecoxal gills each with single filament..........240
239' Filamentous forecoxal gills each with cluster of filaments.........244

Ours are single.

(Before I proceed, let me note that if I find any nymphs with a cluster of filaments on each of the gills -- and I hope that I do -- it may be difficult for me to make any headway.  Identifications in that case require seeing setae on the median ridges of gills -- I don't have the magnification required to carry that out.)

240  Abdominal sterna 6-8 with marking similar to any of Figs 2.386-2.389 ............  241
240' Abdominal sterna 6-8 not exactly matching any of the above variations...........242

Let's look at the sterna.

There clearly are markings on 6-8 (on 5 and 9 as well for that matter), and it looks something like this: (. .) -- a parentheses with two small dots in-between.  That pattern is a very good match for variation 2.388 (p. 127).   On to 241.

241 Abdominal sterna 6-8 with markings similar to any of Figs. 2.386-2.389; abdominal terga yellowish brown to dark reddish brown (with or without lighter mid-longitudinal stripe) .....Isonychia georgiae
241' Abdominal sterna 6-8 with markings similar to Fig. 2.389; abdominal terga light orange-brown with indistinct mid-longitudinal stripe (stripe interrupted by reddish-brown posterior margins of terga 2-9)........ Isonychia obscura

Tough call on the color of the terga since they're really a mix of yellow and brown.  Still, given the match with illustration 2.388,  I'm tempted to propose an ID of Isonychia georgiae.
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Well, it's a start.  Don't expect any dogmatic assertions on species ID for the brushlegged nymphs that I see.  Still fun to see what we come up with.  If the other nymph that I showed you --

had the single filament forecoxal gills, by the way, it would key out to Isonychia serrata ("Abdominal terga with wide mid-longitudinal stripe on terga 1-9").  Pretty much a slam dunk on that one.

Stenacron, Acroneuria arenosa -- and other things at the Rivanna

On the first rock I turned over this morning -- at the Rivanna at Crofton -- there were 3-4 Stenacron nymphs; took me by surprise.  As you can tell by the wing pads on this one, it was fairly mature which made for some very nice photos.

The genus call on these nymphs -- Stenacron -- is fairly easy to make:  they're long and slender, and the gills on terga 1-6 are sharply pointed with the gill on segment 7 being no more than a string.  (See Steven Beaty, "The Ephemeroptera of North Carolina," p. 42)  Here's a photo of one that I found some years ago.

For that matter, the species ID isn't too difficult either.  This is Stenacron interpunctatum.  Two things give it away.  1) The "mid-dorsal streaks" on the abdomen are very distinctive, and 2) the "pale spot anterior to [the] median ocellus [is] approximately as long as wide [and] may be triangular to irregularly shaped."  (Beaty, p. 42)  Bingo.

Beaty notes that S. interpunctatum is "the most common and tolerant Stenacron species in NC": probably the same here in VA.  Still, I think it's one of the more attractive flatheaded mayflies.
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I also picked a couple of common stoneflies (Perlidae) both of which turned out to be Acroneuria arenosa.

I've gone back and forth on the species ID for these nymphs:  A. arenosa or A. evoluta?  The difference is slight.  While both have anal gills -- clearly visible in both of those photos -- the terga on A. evoluta are "uniformly brown" (Beaty, "The Plecoptera of North Carolina," p. 37), but on A. arenosa there's  a "narrow, pale anterior band" on each of the segments.  In the past, I've never seen that "pale, narrow band" so I've been tempted to go with A. evoluta.  But I could easily see it on both of these nymphs.

Acroneuria arenosa, I'm a believer.
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I made one other find, not something I've seen before in the Rivanna.

The dragonfly nymph -- Macromiidae.  Might have to key this one out to the level of genus.  This was a BIG, BIG nymph.
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Need rain!

Somehow I missed this: Clubtail dragonfly, genus Ophiogomphus

I was looking through my dragonfly photos this morning when it suddenly dawned on me that this nymph -- which I found in the Doyles on 9/2 of last year -- was not the clubtail dragonfly that I normally see.  The nymphs that I normally see have wingpads that are parallel to the body: they look like this.

Perplexed, I decided to key out both types and here's what I found.

17a  Naked antennal segment 4 generally about 1/2 as long as hairy segment 3..........Progomphus
17b  Segment 4 of antennae vestigal or nearly so.......18

We've got the latter as I'll show in a moment.  So on to 18.

18a Wingpads strongly divergent........... Ophiogomphus
18b Wingpads laid parallel along back........19

Here you go.

Ophiogomphus for sure.  Hmm...  But I'm quite sure that I thought the other nymph was Ophiogomphus.  Time to explore.  On to 19.

19a Body very flat: abdomen nearly circular in dorsal view; paired tubercles on top of head....... Hagenius
19b Abdomen more nearly cylindrical; no tubercles on head....... 20

19a describes genus Hagenius, and I've found quite a few of those over the years.

We move on to 20.

20a Antennal segment 3 flattened and oval, nearly as wide as long.... 21
20b Long antennal segment 3 more or less cylindrical....... 22

Definitely "nearly as wide as long."  On to 21.

21a Antennal segment 3 widest proximally..... Stylogomphus
21b Antennal segment 3 widest near middle, about 2 times as long as wide and rounded apically....Lanthus

Lanthus.  Got it.  And I find that one a lot.  But for me, Ophiogomphus is a new one.  Have to add that one to my list of taxa.

Macrostemum carolina: no doubt about it

It's the weirdest common netspinner (Hydropsychidae) we see in our streams and I've long wondered about the species ID.

Macrostemum is a netspinner that I've found a number of times in the North Fork of the Rivanna and just last year, I found one in the Rivanna at crofton.  I've posted entries on this one in July, 2011 and August 2012, where I've discussed the genus ID, but to review, there are two features that are fairly dramatic:  1) "the flattened head with a sharp U-shaped carina," and 2) the "dense fringe of setae on the fore tibia and tarsus."  (Glenn B. Wiggins, Larvae of the North American Caddisfly Genera, p. 110 in the 1977 edition)   These.

In the past, using Beaty's "The Trichoptera of North Carolina" (p. 77) I've resisted speculating on species ID, divided between M. carolina and M. zebratum.  The distinction is small: on carolina the tubercles near the eyes are large; on zebratum they're little.   But, our new key -- Larvae of the Southeastern USA: Mayfly, Stonefly, and Caddisfly Species -- seems to resolve the issue in a definitive way.

115  Anterior tubercles above each eye conspicuous ........ Macrostemum carolina
115' Tubercles above each eye inconspicuous .......... Macrostemum zebratum

On the larvae I've found, those tubercles are very, very conspicuous.

Actually, no microscope photo is needed.

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I'd say that mystery's solved.  Macrostemum carolina for sure.