Tuesday, April 22, 2014
This Acroneuria common stonefly from Sunday at Entry Run may be Acroneuria internata, but the jury is out. That's the word from Steven Beaty. They see this same type of Perlid in North Carolina, and they're not really sure what to call it. At the moment they regard it as a particular form of A. abnormis, preferring to take the conservative route. At issue, the thickness of the light colored tergal bands. On A. internata -- you will recall -- they are "of uniform thickness"; on this nymph they are not. The bands are thick in the middle but slightly thinner on the sides.
In the end, there is only one way to know what this is -- a uniquely patterned A. abnormis or in fact A. internata: rear one to maturity and then see what it turns into as an adult. That's the only way we'll know the answer for certain.
I'm not sure I possess the skill set or the equipment to carry this out. But we've now found 3 Isoperla Perlodids and this Acroneuria Perlid for which we don't know the species ID. I might go to NC to see how the rearing is done. Until then: this is the common stonefly (Perlid), Acroneuria sp., possibly A. abnormis, possibly A. internata. That's where it stands. Lots of uncertainty in the entomological world when it comes to species ID of some of our stoneflies.
Off to Oregon on Thursday -- back early next week. If the sun shines in the West, I'll be out seeing what I can find in the streams around Portland.
Sunday, April 20, 2014
Entry Run this morning, where the water was perfect and the insects (nymphs and larvae) were abundant. And I may have found something new.
I took a number of photos of this Perlid: the abdomen just didn't seem right. The genus is Acroneuria, there's no question about it, and it looks a lot like A. abnormis, the species we most commonly see. But I'm not sure that it is: I need to run this one by Beaty. It could be Acroneuria internata. Here's Beaty's description: "A. internata -- male nymphs 15-18 mm, female nymphs 21-24 mm; dorsum of head with interrupted M-shaped head pattern, appearing as a transverse row of 3 light spots in front of anterior ocellus; abdomen banded, posterior margins of tergites light and of uniform thickness; anal gills absent. Recorded from VA, WV, and GSMNP."("The Plecoptera of North Carolina," p. 14)
The size of this nymph was about 18-19 mm -- though it's not completely mature. The "M" pattern on the head is clearly interrupted, with three pale "slashes" in front of the anterior ocellus. And, it seems to me, that the light bands on the terga are indeed uniform in thickness. Here's a close look.
It is that feature -- the uniform thickness of the light bands -- that distinguishes this nymph from A. abnormis. Beaty on A. abnormis -- "posterior margins of abdominal tergites light, dark tergal bands irregular." They look like this.
I'll get back to you when I hear back from Beaty.
There were all sorts of insects this morning on the rocks and in the leaf packs. Here's a sample of some of the neat things I saw.
1. A beautiful Giant stonefly, Pteronarcys biloba. Fully mature: note how the tips of the wing pads are black, not sure I've seen that before. (Note the small minnow mayfly -- Baetis tricaudatus -- clinging to the right foreleg.)
2. There were Peltoperlids (Roach-like stoneflies) all over the place. Those that I checked were genus Tallaperla. On Tallaperla nymphs the "thoracic gills [are] double" and the "posterior edge of [the] prosternal plate [is] mostly straight across... [while the] metasternal plate [has] long posterior wings." (Beaty, "The Plecoptera of North Carolina," p. 12) Here's a good look at both of those features.
3. A gorgeous Perlodid stonefly, Diploperla duplicata.
A number of insects enjoyed crawling on this one. Two Peltoperlids...
and a little spiny crawler.
5. The most common insect today: flatheaded mayfly, Epeorus pleuralis. Saw a lot of them ready to pop (black wing pads).
6. And another common insect today: Perlodid stonefly, Isoperla montana/kirchneri. No surprise there. Note that the wing pads are starting to darken. Abdomens are kind of a butterscotch color.
7. And a third insect that was common today: freeliving caddisfly larva, Rhyacophila fuscula. They're getting long and fat.
But the one we need to ID for sure: common stonefly, possibly Acroneuria internata.
It's the best time of year to get to the streams -- and not just for seeing the insects. Trillium?
Thursday, April 17, 2014
Back to Sugar Hollow today, to one of my favorite streams. And I saw a lot of these nymphs: the Green Stonefly (Chloroperlid), genus Sweltsa. Note how these nymphs differ from the Haploperla Chloroperlid we found yesterday.
Color, -- greenish brown: tails -- medium length, slanting away from the body; size when mature --- ~7 mm; wing pads -- inner margins close to parallel to the line of the body.
Color -- golden brown; tails -- short, point straight back from body; size when mature -- 7-8.5 mm; wing pads -- inner margins diverge from the main line of the body.
"Mature" was the name of the game at this small stream today. Beautiful insects with black wing pads that by now could be flying around.
1. Pronggilled mayfly, Paraleptophlebia sp. (mollis?)
2. Flatheaded mayfly, Epeorus pleuralis
3. And the flatheaded mayfly, Maccaffertium merririvulanum. Not quite mature, but the wing pads are long and dark brown: size, close to 16 mm.
And the defining feature -- the pale "V's" on terga 5, 7, and 8.
Only found in pristine, headwater streams. Like the one we went to today.
Of course not everything was mature. Even here the spiny crawlers (E. dorothea) are taking over the stream by the hundreds, but they're still pretty small. And I did find one real small Perlodid.
It has a long way to go before it matures into this --
one of our unknown Isoperlas.
One of my favorite sights in the spring in Virginia -- redbud trees. Our flowering trees are in bloom wherever you look.
Wednesday, April 16, 2014
After two inches of rain yesterday I didn't hold out much hope for finding good insects this morning -- but I was surprised.
In the photo at the top of the page, the Green Stonefly (Chloroperlid), Haploperla brevis. Though Beaty says this genus and species is "relatively common" ("The Plecoptera of North Carolina," p. 9), this is only the second one that I've found.
Beaty describes Haploperla in the following way. "Nymphs ~ 7 mm; cerci without dorsal or ventral intercalary hairs, setae at apex of cercal segments only; pronotum with sparse setae, longest and most numerous at anterior corners; long pronotal fringe hairs are at least 0.3 - 0.4 times the pronotal width; inner margin of hind wing pads subparallel to body axis; pronotum and tergites lightly setose; fore leg with sparse fringe of long setae on tibia; body light brown, nearly concolorous." "H. brevis -- fits genus description." Elsewhere, the NC tolerance value is given as 1.4.
1. Our nymph measured about 6 mm.
2. The lack of intercalary hairs on the cerci can be seen in the following photo.
3. And here is a view of the long setae on the corners of the pronotum. I'd agree that the longest hair that we see is .3 - .4 times as long as the pronotal nymph.
4. The hind wing pads -- and the primary wing pads for that matter -- are indeed subparallel to the body, but we can only see that in a microscope view. (Note: in many keys, this feature is the defining feature of this genus.)
5. And here we can see the "sparse fringe of long setae" on the fore tibia.
Haploperla brevis. Made the whole trip worthwhile.
But I also found the freeliving caddisfly larva Rhyacophila carolina for the first time this season at the Whippoorwill Branch.
R. carolina is distinguished by its golden brown head, the lack of ventral teeth on the anal claw,
and the fact that the head is very wide at the rear -- in fact at that point it's almost as wide as it is long.
R. carolina is part of a group (the R. carolina group) that is found predominantly in the southeast. The group includes R. fenestra/ledra, a species we also see in the summer. This one.
TV for R. carolina is 0.4.
Another beauty this morning, a fairly mature common stonefly, Eccoptura xanthenses. Note how the wing pads are long, and curved at the rear. This one measured about 17 mm.
But the most common insect today -- the spiny crawler, E. dorothea. Get ready to be overwhelmed if you're out there taking your samples.
For the species ID, you need a close view of the terga. There are no tubercles (projections) on the rear edges of the terga on the nymphs of this species.
But this one was special -- Haploperla brevis.