Saturday, April 22, 2017

Project for a rainy day: re-examining Amphinemura species ID

Rain at last, and it's supposed to continue through Tuesday.  Our streams really need it.

You'll recall that I found quite a few Amphinemura Nemourids last week at Buck Mt. Creek.  On Tuesday, I went to the Rivanna and they were in there as well.

Some time ago I worked on Amphinemura species ID and reached the conclusion that those that I've found in our streams are Amphinemura delosa.    This was based on the description of A. delosa found in a 1971 article by P. P. Harper and H. B. N. Hynes: "The nymphs of the Nemouridae of Eastern Canada (Insecta: Plecoptera)," Canadian Journal of Zoology, 49: 1129-1142.  Let me review their description (their words cited in BOLD) noting those features on the nymphs that I've found this week and last.  (See p.1131 of their article.)

1. Total length of mature nymph, 5-6 mm.  The nymphs that I found were all 5.

2.  Color medium to dark brown, head darker; antennae pale, first few segments darker; Yes.

3. legs brown; ... cerci pale, first few segments darker;  Yes.

4. Short bristles covering head capsule, those behind eyes longer and stout.  Very clear.

5. Pronotum rectangular, nearly as broad as head, covered with short bristles and hairs; pronotal fringe well defined, consisting of long pointed bristles.  They are indeed long and pointed.  Not real easy to see the bristles and hairs on the pronotum itself with all of the sand and silt on the nymph.

6. legs with long stout bristles, the longest femoral bristles longer than the greatest width of the femur.  They don't seem quite that long on my nymph, but I think they're close enough.  This nymph was still immature.

7. a few long hairs on the tibiae but no tibial fringe.  Yes.

8. prosternal gills in four tufts; distance between the median tufts about twice that between the median and lateral tufts; each tuft comprising about eight (in mature nymphs) filaments forming a whorl around a central axis.    That's a match for our nymph.

9. Finally, abdomen covered with long bristles, the longest marginal bristle longer than the mid-dorsal length of the corresponding tergum.


Looks like a slam dunk to me.  But just to be sure, I thought I'd see what Steve Beaty says in his latest work on "The Plecoptera of North Carolina" (Version 4.0, 2015).  Gives me pause.

To begin with, he notes that four species of Amphinemura have been found in North Carolina: appalachia, delosa, nigritta, and wui.  (Harper and Hynes, by the way, have described A. nigritta and A. wui but not A. appalachia. A. delosa and A. nigritta are very similar, but not exactly the same.)  But he cautions those of us using his guide to leave Amphinemura ID at the level of genus.  I'm not exactly sure why -- I need to check in with him on this matter.  I suspect he feels that we need to be cautious until the nymphs of all four species have been fully described.  Then again, he may question the reliability of a study done nearly 50 years ago.  There is good news: B.P. Stark (of Stewart and Stark) is apparently preparing a "nymphal key to the eastern species of Amphinemura," but it will not include a description of A. appalachia.  Bummer.

All things considered, I think that at the moment the safe thing to call the nymphs I've been finding is Amphinemura sp. (delosa?).  I'll let you know if that changes.

Saturday, April 15, 2017

Isoperla davisi at Buck Mt. Creek

A species of Isoperla that I haven't seen for four years -- Isoperla davisi -- one that I've only seen at Buck Mt. Creek.   Better review how we arrive at the species ID.

We rely on the patterns we see on the abdomen and the head.  "pre-emergent nymphs 7.0-8.0 [mm].  Lacinia recedes from base with 6-8 stout marginal spines below subapical tooth; both pale area anterior to median ocellus and pale ocellar spot enclosed; transverse brown bar on anterior frontoclypeus wider than brown area that encloses the anterior pale median area." (Steve Beaty, "The Plecoptera of North Carolina," p. 59)

Our nymph is 8 mm long.  The lacinia is as described,

as is the head pattern.

Beaty continues: "dorsum of abdomen with distinctive longitudinal '5-lined' banding; median and sublateral bands darker and usually narrower than submedial bands and with intervening pale narrow lines."  

If you go to NatureServe Explorer ( and enter "Isoperla davisi," you'll see that the common name for this species is "Alabama stripetail."  Curiously, they fail to note that this species is found in both Virginia and North Carolina (here only listed for Alabama, Florida, and South Carolina.)

Good to see this one again.


It was a great day at Buck Mt. Creek.  Lots of insects around, including a bunch of Nemourids, the genus we see in the Spring -- Amphinemura.  (Amphinemura delosa.)

These are the Nemourids with the "cervical gills," which makes them very distinctive.


I saw a lot of Amphinemura, but without any question, the bug of the day in terms of sheer numbers was the small minnow mayfly, Plauditus dubius.   I saw both male and female, and almost every nymph that I saw had black wing pads = ready to hatch.

They can be distinguished by gender with a quick look at the eyes -- big eyes on the males (first photo) -- but the abdominal patterns differ as well.  While the pattern is hard to see on our male since it's so black, we can see the key feature on the female.  "female -- median spots on terga 2 and 6."  (Beaty, "The Ephemeroptera of North Carolina," p. 22)

The dark median band on the tails is present on both male and female.

The weather's been great so I hope to get out a lot more.   The warm temps and low water we've had most of the year, mean that things are ahead of where we expect them to be.  To wit, I'm already finding Isoperla holochlora nymphs.  Very early.

Tuesday, April 11, 2017

Montana Part II.: Isoperla sp. and Skwala sp.

June is the time to fish "Yellow Sallies" in western Montana, and it looks to me like this is the nymph providing that hatch.  There are already a lot of these critters in the Bitterroot River, and last spring I found them in the Blackfoot and the lower Clark Fork (see entries of 4/5 and 4/6/16).   It's a nymph, as I noted last year, that looks a lot like Isoperla roguensis, but roguensis has not been found in Montana.  What has been found in Montana is Isoperla fulva, and as nymphs I. fulva and I. roguensis apparently cannot be distinguished.  (See John Sandberg's "The Isoperla of California (Plecoptera: Perlodidae): larval descriptions and a key to 17 western nearctic species," Illesia, 7:22 [p. 245].)  Be neat to find some way to pin down the ID.


But this is the reason I go to Montana at this time of year.

The Skwala!  While we didn't take a lot of our fish on dry flies this year, we certainly saw plenty of Skwalas flying around and there were loads of them crawling around on the rocks in the water.

Not all of them were mature, so there will be Skwala fishing this year right into May.

Sunday, April 9, 2017

Back from Montana with some beautiful insects

I was fishing in Montana last week -- and looking for insects -- and I found some beautiful nymphs, including two large winter stoneflies (Taeniopterygidae) that I've not seen on previous trips.

Number one is this beautiful nymph that I found last Wednesday on the Bitterroot River.  Personally, I think the colors are stunning, and as you can see by the black tips on the wing pads it was fully mature.

From what I can tell, there are five species of "Willowflies" (Taeniopterygidae) in Montana ( Taenionema pallidum (Common Willowfly), Taenionema pacificum (Pacific Willowfly), Oemopteryx fosketti (Saskatoon Willowfly), Taenionema uinta (Uinta Willowfly), and Doddsia occidentalis (Western Willowfly).

As will become clear in a moment, this is not a Taenionema nymph.  Taenionema nymphs, for one thing, are dark brown in color as we have seen with the species we find in our own streams, Taenionema atlanticum.  This one.

That means our nymph is either Oemopteryx fosketti or Doddsia occidentalis.  Both Doddsia and Oemopteryx are described in detail in Stewart and Stark (Nymphs of North American Stonefly Genera, pp. 227-235).   The nature of the laciniae and the mandibles is important in deciding on identification -- unfortunately, my microscope won't allow me to see them very well.  However, there are two other things to consider.  1) The mesosternums aren't the same.  On Doddsia, the stem of the mesosternal ridge is "about equal in length to each arm"  while on Oemopterx, the stem is considerably shorter.  This looks like a Doddsia nymph.

And 2) the shape of the ventral plate is on Doddsia is "semi-ovate", not so on Oemopteryx (see the illustrations on pp. 231 and 234).  We have an oval plate on this nymph (note how the top edges curl in).

While I can't be sure of my identifcation, if I had to guess, I'd say this is Doddsia occidentalis, the Western Willowfly.


This is nymph number two.

While I found nymph number one in the big, wide Bitterroot River --

nymph number two -- and I must have picked up 50 of them in a matter of minutes -- was in a small stream by our hotel, Grant Creek.

I'd bet the house that these were Taenionema large winter stoneflies.

The color alone is a pretty good sign.  The "brown body color" -- noted in every key that I've seen -- is noted by Stewart and Stark (p. 241) as one of the key "Diagnostic Characters".    Again, I can't see the laciniae and mandibles as I would like, but I can note three other things that help with this genus ID.  1) Beaty notes ("The Plecoptera of North Carolina," p. 23) that the "posterior margin of [the] pronotum [is] wider than [the] anterior margin."  Pretty clear that it is.

2) the sternal plate of the male is "broadly triangular in posterior half and bearing short erect hairs in posterior two-thirds." (Stewart and Stark, p. 241) That's a match.

And 3) there's the legs.  "Legs with continuous, silky dorsal fringe, sometimes sparse on tarsus." (Stewart and Stark, p. 241).  That's also a match.

Taenionema for sure.  Which one -- pacificum, uinta, pallidum? -- I haven't a clue.  I can't find any keys that take this to the level of species.  We need Steven Beaty to move to the West.  (:


The fishing was great.

The Skwala stoneflies were hatching.  Photos of Skwala nymphs and an adult in my next entry.