Tuesday, July 31, 2012
This is the common netspinner (family: Hydropsychidae) that I found in Roaring Creek (between Catawissa and Danville) on July 21st. I've now been able to identify this as Ceratopsyche sparna. However, there is an issue with the name of the genus and let me begin by clarifying that matter.
The species name you find for this larva will depend on the source that you use. 1) Steven Beaty ("The Trichoptera of North Carolina") identifies this as Ceratopsyche sparna. 2) On Bugguide.net -- and elsewhere (see, for example, Rick Abad & Andy Rasmussen's "Preliminary Key for Species for Larvae of Florida Hydropsyche" -- online pdf)-- it is identified as Hydropsyche sparna. 3) But in Schuster and Etnier's "A Manual for the Identification of the Larvae of the Caddisfly Genera Hydropsyche Pictet and Symphitopsyche Ulmer in Eastern and Central North America" -- also online -- this larva is labelled Symphitopsyche sparna.
On this problem of genus naming, Steven Beaty has this to say: "Systematically, Ceratopsyche is also recognized as Symphitopsyche, Hydropsyche morosa group, or Hydropsyche bifida group. There are still some systematic experts that dispute Ceratopsyche as a separate genus arguing that it is, at best, a subgenus of Hydropsyche." Obviously there is an issue here that, as an amateur, I cannot resolve. However, I can tell you why Beaty and others (including Merritt, Cummins and Berg) treat Ceratopsyche as a genus that stands on its own even though the two are closely related.
Ceratopsyche and Hydropsyche larvae share the following features: 1) the fore trochantin is forked --
and 3) in both cases, the submentum is notched apically.
How do they differ? To put it simply, Hydropsyche larvae are "hairy," Certaopsyche larvae are not. Look at the dorsum of the abdomen on this Hydropsyche larva that I collected last year. (Click on the photo to enlarge it.)
Now have another look at the abdomen on the nymph on which we are working.
While both larvae have what are called "club hairs," in addition, Hydropscyhe larvae have "minute spines and scale hairs," and it is the "scale hairs" that gives the Hydropsyche its "hairy" appearance. There is a good illustration of this in Merritt, Cummins and Berg, An Introduction to the Aquatic Insects of North America: see p. 495, Figures 18.89 (Hydropsyche setation, abdominal tergum VIII), and 18.90 (Ceratopsyche setation, abdominal tergum VIII).
So there you have it. That Ceratopsyche is a genus that stands on its own as clearly distinct from Hydropsyche is a matter that's still being debated. But in this entry, I'll use Ceratopsyche, following Beaty, and following Merritt, Cummins, and Berg.
Now, on to the ID of our larva as Ceratopsyche sparna. Beaty describes C. sparna in the following way:
"...head brown with 3 faint pale spots, one central with others anterolateral to the central spot." That's it. Let's have a look.
And even closer (I've numbered the spots) --
I'd say that's a match. But the description in Schuster and Etnier's "Manual" (online at:http://www.epa.gov/bioiweb1/pdf/EPA-600-4-78-060AManualfortheidenticationofthecaddisfly_shusterandetnier.pdf) -- where this species is called, you will recall, Symphitopsyche sparna -- the description is much more detailed. Let me read you at least part of that description for verification. "Head, nota and all leg segments golden in color; dorsum of head slightly darker golden brown. Frontoclypeus [essentially the top of the head] with a pair of yellow spots anterolaterally, often with an additional single spot in center of the sclerite."
and again --
They continue, "Labrum brown and covered with short, black setae; the lateral brush consisting of long, yellow setae. ... Mandibles yellow and edged in brown. Venter of head predominantly yellow with some brown patches on stridulatory surface." That the labrum is brown we can see from the previous photos. For the rest, we look at the following picture of the underside of the head.
Check. "Prosternum with the posterior border black. Poststernal plates dark brown and solidly sclerotized."
Check. And I think that's enough to wrap it up. Our nymph is Ceratopsyche sparna (or Hydropsyche sparna), and, by the way, this is a relatively intolerant common netspinner, with a tolerance value, in North Carolina at least, of 2.5.
One last photo.
Sunday, July 29, 2012
It's July 29th, but when I stepped into the Rapidan River this morning, there they were: six Odontocerid cases on a single large rock. But everything else has been early this year -- so why not? I didn't see them last year until September 18th. The nice thing about this case-making caddis is that you don't have to hunt to find them: you'll see their tube-like cases made of pebbles and sand on the tops of rocks where the larvae are grazing. And you can pick them up firmly with tweezers: the cases really are "strong," you're not going to crush them.
The genus is Psilotreta: for species ID, we have to wait until they're fully mature -- these clearly were not.
(For the five species of Psilotreta found in the southeast, look at Steven Beaty's "The Trichoptera of North Carolina.")
But the case-maker that still covers the rocks in the Rapidan River is the "Humpless case-maker" -- family, Brachycentridae. The species we find here is Brachycentrus appalachia, on which see the entry of 7/10.
I got some nice photos of a fair-sized one today, sticking its head out of its 4-sided case.
And yes, the larval body really is green!
There were lots of common netspinners present this morning -- as we're seeing at the moment in all of our streams -- fingernet netspinners as well (genus Dolophilodes). And I saw a good number of flatheaded mayflies: Epeorus vitreus and a few Maccaffertium ithaca. But the mayfly I was hoping to see was the small minnow mayfly, and I was not disappointed. I found a few A. nadineae nymphs and a couple of Plauditus dubius females. The latter surprised me -- I thought this species had hatched by this time of the year.
A. nadineae and P. dubius in the same photo:
Acentrella nadineae (male):
Plauditus dubius (female): (Note the medial band on the tails.)
Stoneflies? I'm starting to see a lot of small to mid-sized Perlids, as we should at this time of the year, and I also continue to see some genus Perlesta Perlids in the Rapidan -- elsewhere, this genus has hatched. But the prize stonefly of the day was another BIG (1 1/4"? 1 1/2"?) Paragnetina immarginata.
Magnificent! These are hatching right now as "Golden Stones" -- in fly fishing terms -- and I saw a lot of "shucks" on rocks to prove it. This one will surely be joining them soon.
(Below: two of the Odontocerids that I picked up when I walked into the stream.)
Friday, July 27, 2012
The very first A. nadineae small minnow mayfly I found, I found last year on June 23 in the Doyles River at Doylesville (off Blufton Road). This one.
Today I returned to that site and found some again -- one was fully mature with black wing pads.
But it was the nymph in the photo at the top of the page that really drew my attention because of the light stripe that runs down the dorsum. Some more photos.
This is an A. nadineae pattern that I've seen only one time before -- last year on July 2 at the Lynch River.
And note, as well, the markedly greenish body color on that Lynch River nymph.
Note how different this nymph appears than one of the nymphs that I found at the North Fork of the Moormans just a few weeks ago on July 6.
I assure you that all of the nymphs in the photos above are A. nadineae small minnow mayflies: all have the key features we use for this ID. Those features are: 1) at least some of the terga are tinged red/orange; 2) the gills have a distinct "baso-medial" (extends from the base of the gill through the middle of the gill) splotch of gray pigmentation; 3) there are orange/red dots at the tops of the wing pads (though these are indistinct on mature nymphs); and 4) the fore femora are long, slightly longer than the fore tibiae and tarsi combined. Let's have another look at those features.
Why don't all A. nadineae nymphs look the same? Clearly, part of this has to do with the level of maturity. All mayfly and stonefly nymphs, as we know, darken as they mature, and the orange/red markings on mature A. nadineae nymphs are harder to see.
But why are some fairly green while others are orange? Why do some seem to have a pale stripe down the middle? Why are the orange/red markings more pronounced on nymphs in one stream than they are on nymphs in another. On that point, by the way, have a look at the A. nadineae nymph that I found in Pennsylvania last week.
Red and orange dots and stripes and splotches on the terga, the thorax, the wing pads -- even the head!
I can't really answer my questions, but we do well to remember that colors and patterns do vary by stream, and that we always need to rely on morphology to determine species identification. Surely habitat -- types of vegetation in the water, types of rocks in the substrate, water chemistry -- accounts for some of these variations. And "camouflage" is always a relevant factor. Nymphs do evolve different colors and patterns for their own protection.
Whatever the explanation, or explanations, for the variations we find -- these are some of the loveliest
small minnow mayfly nymphs we see in our streams in the course of the year.
(Two of the nymphs from this morning huddle together and pose for a picture.)
Thursday, July 26, 2012
Two of the nymphs I was expecting to see in the Rivanna at Crofton this morning: a broad-winged damselfly, Haeterina americana, and a small minnow mayfly, Heterocloeon curiosum. Here is a better look at both of these insects.
While I can find more small minnow mayflies in the Rivanna at Darden Towe Park, when I'm after damselflies and dragonflies, I go to Crofton. The damselfly I often see here is the narrow-winged damsel (Coenagrionideae) -- but I only saw small ones today; the most common dragonfly that I see is the Corduliade, Neurocordulia obsoleta (the "Umber Shadowdragon") -- they were all over the river!
But on to new things. There are three taxa that I have only seen in the Rivanna at Crofton, and to those we turn our attention. Number one, the "little stout crawler" mayfly: the "trico" to fly fishermen, but in entomological terms, family: Leptohyphidae, genus Tricorythodes. (I've seen the family and genus names reversed, by the way, with the "genus" being Leptohyphus. I guess the pros can't make up their minds.)
Some photos, which are not terribly good for two reasons: 1) these little nymphs are almost always covered in silt, and 2) they're little, 3-4 mm.
Tricos are easy to ID with minimal magnification. They have large, triangular, operculate gills that reach back from segment 2. These (to me they look like "chaps"!):
In both of the photos above, you can see them sticking out from the sides of the abdomen, and in the following photo, I've pointed them out.
The "trico hatch" is not a favorite of fly fishermen -- the adults, as you might expect, are tiny! But when the trout are on them, you'd better have a good imitation. It's the only thing the trout will go after.
The second taxon that I found this morning that, to date, I have only seen at this spot in this river is the common stonefly, genus Agnetina. And, to date, I have only seen nymphs that are immature and therefore quite small. This one measured 3.5 mm.
Agnetina nymphs differ from Paragnetina nymphs (on which see the last entry) by having subanal gills. Both genera have a complete setal row on the occipital ridge (back of the head). The row of setae is easy to see on this nymph; the subanal gills are not (the nymph is too immature). In the photo below, the subanal gills are the light gray patch between the cerci.
I'd like to ID this nymph to the level of species, but it's too immature to make that determination.
Head pattern is a crucial factor in species ID, and the pattern here is not yet fully developed. That being said, I think there's a good chance that this is A. flavescens. Clearly, I need to return to this site in the winter and find a specimen that's fully mature.
Finally, there is another taxon that I have only seen at this location: the gilled snail Hydrobiid. Here's a bunch that ended up on my tray.
If you look closely, you can see the tentacles protruding from almost every one of these shells. This is a tiny, tiny snail: these shells were 1-3 mm high. If you don't know what you're looking for, you might think you had picked up some very small pebbles -- until you see the tentacles sticking out as the snail moves across the tray.