We seem to be seeing a lot of pronggilled mayfly nymphs this summer, so I thought I might review and comment on the problem of species identification. Steven Beaty's advice is "LEAVE AT GENUS" for the identification of Paraleptophlebia ("The Ephemeroptera of North Carolina," p. 79), and for very good reason. The most detailed species descriptions I've seen rely on minute details of the labrum, mandibles, maxillae, and hypopharnyx -- and I can't determine those things with the microscope that I use. (See R.P Randolph and W.P. McCafferty, "First Larval Descriptions of Two Species of Paraleptophlebia," Entomological News, 107 (4), pp. 225-229, 1996.) I'll focus on description of observable features -- but even there clear distinctions can be made.
Let me start with a common distinction -- the nymph has "branched" or "unbranched" gills.
I've found two different nymphs that share this feature. The first, the one at the top of the page. This one.
I think this nymph is fairly common. There are a lot of these at the Rapidan River and in South River as well. This one from the South.
There are three distinguishing features: 1) the gills are branched (Randolph and McCafferty, "middle trachea with dark lateral branches"); 2) there are posterolateral projections/spines on terga 8 and 9: and 3) there are pale medial marks on terga 3-7. To wit:
This is a nymph I usually see from winter through early spring.
The second nymph with branched gills that I've seen is one that my friend has found in Sugar Hollow.
She found this on on 1/23/15, and note that the wingpads are already long, so it is also around in the winter. This nymph/species also has branched lateral gills and posterolateral projections, but the abdomen is virtually devoid of a pattern (except for, possibly, a pale lateral stripe?).
Possible species IDs? Knopp and Cormier (Mayflies, p. 269) list two Eastern species with branched gills -- P. adoptiva and P. mollis -- but neither one has posterolateral projections. Unzicker and Carlson (Aquatic Insects and Oligochaetes of North and South Carolina, p. 3.60) list these same two species as "branched." Randolph and McCafferty, on the other hand describe a third species -- P. assimilis -- as having both branched gills and posterolateral projections. So a possibility there.
Here I have four nymphs/species to describe. The first, the one I think is P. guttata.
Found this one at the Rapidan River, and this one
just two weeks ago in Sugar Hollow. (My friend found another last week.) There's not much to describe, not much of a pattern on the abdomen or the head. The gills are lack lateral branching, and, importantly, there are no posterolateral projections on terga 8 and/or 9.
This matches the description given by Knopp and Cormier, and my photos match those posted by Donald Chandler on DiscoverLife (http://www.discoverlife.org/mp/20p?see=I_DSC155&res=640).
Detailed microscope work would need to be done to be certain of our ID, but at the moment I'd bet on P. guttata.
Next up, that little nymph I found yesterday.
and there were no posterolateral projections that I could detect (very small nymph, 5-6 mm). To me, the abdominal pattern is very unique.
Note how the anteriors of terga 2-7 are pale, and those pale areas extend down to the sides. This is the first time that I've seen this pattern.
Number 3, a nymph that my friend found earlier this month,
and similar to it, one of the nymphs that I found on June 6.
Unbranched gills, posterolateral projections present, and, we can see those pale parentheses marks
( ) on some of the terga. Also worth noting, the legs -- on her nymph at least -- seem to be dark in color, possibly banded.
One more, another nymph found by my friend in the very pure stream that flows by her house.
I don't think we know if this one had posterolateral projections, but the abdominal pattern is very distinctive. We can again see the parentheses marks on the terga, but in addition, the posterior edges of the terga are light and they project anterolaterally.
If we set aside the guttata, can we suggest IDs for the other three nymphs? There's a possible ID for this one.
It's a pretty good match for P. debilis which has pale legs with dark bands (Unzicker and Carlson, p. 3.60). Chandler has posted a photo of this one -- http://www.discoverlife.org/mp/20p?see=I_DSC154&res=640 -- and there too, there are distinct pale markings on terga 7-10. For the rest, more work is needed. Randolph and McCafferty describe a species with unbranched gills and posterolateral projections -- P. jeanae. A possibility there. And Unzicker and Carlson note two other Eastern species with unbranched gills -- P. volitans and P. moerens. Both are noted as having legs that are "uniformly brown or nearly so."
That's as far as I can go at the moment. Intriguing. I must confess that before we started checking this spring, I assumed we only had a couple of Paraleptophlebia species here in our streams. No longer the case. I'll be checking things closely as the summer proceeds. Beaty lists 11 possible species for us to find. But, not all of those nymphs have been described, and some are rare, "vulnerable to extirpation." Between Unzicker and Carlson and Randolph and McCafferty, nine species can be keyed out. But I'll have to leave certain IDs to the professionals with their professional microscopes.
Paraleptophlebia nymphs are intolerant and are only found in good streams. Tolerance Value for the genus in general is 1.2.
CORRECTION (6/22/17): In my description above of P. guttata, I incorrectly said that there are no posterolateral projections on segments 8 and 9. There is a projection on 9 but none on 8. (See Knopp and Cormier, p. 269) This is easy to see in the photo my friend took of a nymph that she found.