Flatheaded mayfly: Heptagenia marginalis

The Rivanna River in Charlottesville has been high and muddy most of the summer.  Some of the time that could be blamed on heavy rain -- but not all of the time.  Somebody was doing something upstream, not sure what.  In any event, it now seems to be dropping and clearing so I went to Darden Towe Park this morning to see what I could find.

There were a number of insects to photograph, but these pictures turned out the best.  Flaheaded mayfly: Heptagenia marginalis.   While I found this nymph once in the Moormans, I've seen it more often in the Rivanna at Darden Towe and always at this time of year.   Heptagenia nymphs have fibrilliform behind gill number 7 (it's absent on 7 on Leucrocuta and Nixe).   For the species ID, all we have to see are the dark sublateral streaks on the terga.

Tolerance value is 2.2 -- not all that bad for the Rivanna.  Found two.

I'm not sure what explains the bright yellow marks on one of the nymphs (terga 1, 8 and 9) but not the other.  Guess it could be a gender distinction.

A change in the pronggilled mayfly genera: new genus, Neoleptophlebia

I just learned of this change Sunday night.  Pronggilled mayflies with tracheal branching on the gills have been put into a new genus -- Neoleptophlebia -- moved from Paraleptophlebia.  Of the pronggilled nymphs that I've found, that means assimilis -- pictured above -- is now Neoleptophlebia assimilis.

Also now considered Neoleptophlebia, and additional species that we might very well find, are adoptiva, mollis, and swannanoa.

Unaffected by this are the other species I've found, those without tracheal branching, guttata, strigula, and what I think is jeanae.  They remain genus Paraleptophlebia.    These.

P. guttata

P. strigula

P. sp. (jeanae?)

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The complete list of North American Ephemeroptera (mayflies) can be found at:
https://www.entm.purdue.edu/mayfly/na-species-list.php.

Something new! An "armored mayfly" (Baetiscidae), Baetisca berneri

I just wasn't ready for this one.  In all of the years I've been out on the streams, this is the first time I've managed to find one of these nymphs.  A Baetiscidae -- armored mayfly -- which keyed out to Baetisca berneri.  I never thought I would see one.

Habitat, according to Beaty, is "Lotic, partially buried, often in shallow sandy or gravelly riffles or in edge vegetation."  ("The Ephemeroptera of North Carolina," p. 73)  And that's pretty much where I found it, by stirring up rocks and sandy gravel in a small riffle close to shore -- Rapidan River.

Genus ID: "Anterior margin of head with medial frontal projection or with anterolateral genal spines; enlarged thoracic notum fused between wing pads and forming a shield or carapace-like projection which is extended to abdominal segment 6; gills concealed beneath thoracic shield; three caudal filaments, short; body typically light brown with variable dark pigmentation."  (Beaty, p. 73)

All visible here, and this one has the genal spines.

On to the species -- it's Baetisca berneri, which is "Uncommon and very intolerant," according to Beaty.  (Would we expect anything less from the Rapidan River?!)

berneri -- nymphs 7.5-11.5 mm; genal spines present; caudal filaments prominently banded with dark brown at base; body pale with variable speckling, an interrupted dorsomedial line on abdomen; ventral surface may be speckled and brown.

There's no question about the ID, but this was a much smaller nymph than Beaty describes: it measured a mere 4.5 mm.  Sure wish it had been bigger, my photos would be much better.  As it is, I'm surprised I got any photos at all.  This little guy -- and with those big red eyes it is a "guy" -- kept darting around my petri dish making it very hard to focus.  But I still got some decent shots.

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Pretty exciting.  However, the Rapidan is very low -- it could use a whole lot of rain.

Have to post a retraction: clearly not Isonychia georgiae

The Isonychia nymphs that I found at Buck Mt. Creek, I'm afraid, were something other than I. georgiae.  I made a basic mistake.  What I thought were single filament forecoxal gills were, in fact, the labial and maxillary palps.

These are the forecoxal gills,

and as you can see they are not single filaments, what we find is a "cluster of filaments."  That eliminates the following species from consideration for the species ID: georgiae, obscura, serrata, hoffmani, and similis.  With the cluster of filments, it could be Isonychia sayi were there no "marginal spines on the distal margins" of the abdominal gills, but clearly such spines are present.

That being the case, our key -- Larvae of the Southeastern USA: Mayfly, Stonefly, and Caddisfly Species -- gives us the following options: 1) "Gils 6-7 (gills on abdominal segments 6-7) with row of minute robust setae along entire length of median sclerotized ridge," or 2) "Gills 6-7 without distinct row of minute setae on median sclerotized ridge." (Larvae, p. 128)  This is the ridge:

and I cannot see what is or is not on that ridge without greater magnification than I can get with my microscope.

So, back to the drawing board.   I cannot determine the species.  Were I to speculate, I'd go with Isonychia bicolor.  That is based on the fact that the unusual abdominal pattern we see on this nymph --

closely resembles Fig. 397 in our key (p. 129) which is an "I. bicolor variant,"  a species that is "widespread in the Southeast." (p. 128).  Best we can do at the moment.

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.