Wednesday, June 18, 2014
A nice find at Buck Mt. Creek: the Green Stonefly, Alloperla
I wasn't sure what I'd find this morning at Buck Mt. Creek. Surely the flatheaded mayflies, Epeorus vitreus, and maybe some small, small minnow mayflies since we've moved into the hot, humid weather of summer: I found both. But the find of the day was this maturing green stonefly (Chloroperlidae), genus Alloperla. I've seen them before, but only a couple of times.
Let's look at Beaty's description. "Genus Diagnosis: Nymphs ?? mm; pronotum with setae usually restricted to corners; mesal portion of posterior margin of abdominal sternite eight lacking setae; distal end of cerci with feather-like surface (in lateral view) due to 2-6 long setae between apical coronas." "Primarily found in gravel and riffle areas of small to medium streams..." "Mainly collected January through May in the Mountains. Uncommon." ("The Plecoptera of North Carolina," p. 9)
He adds: "North Carolina has at least seven species of Alloperla of which the nymphs of most of these species are undescribed (including A. lenati). So we leave the description at the level of genus.
1. This is a very small stonefly: this one measured a mere 6 mm.
2. Despite the small size, I was able to see the setae at the pronotal corners.
3. I could not get a good photo of the 8th sternite.
4. On the "feathery" tips of the cerci (tails), this is the best I could do, but you can see the long setae "between the apical coronas".
Pretty special. Always nice to find something "uncommon," and given the small size of this nymph, I was pleased with my photos.
The other stonefly I found is one that we commonly see at this time of year: the "common" stonefly (Perlidae), genus Perlesta. Found two.
I don't know if I've called this our "June" Perlid before, but the name is certainly fitting. It's a univoltine Perlid, meaning there's a single generation each year, and we see them from May to July. Like the Alloperla I found, this Perlid cannot be ID'd to the level of species. However, Beaty does say that some species are "currently being associated" ("The Plecoptera of North Carolina, p. 19), so I might check in with him to see if any progress has been made in that direction.
Genus Diagnosis: Nymphs 8-12 mm; setal row on occiput complete, sinuate, and with irregular gaps; abdomen with numerous short, stout intercalary setae, often with pigmented bases giving abdomen a speckled appearance; anal gills present; body covered with fine, dark clothing hairs. (p. 19)
It's a no brainer: they're genus Perlesta.
But I did find Epeorus vitreus, and I did find some small minnow mayflies including the first Acentrella nadineae of the season. We'll see plenty of them throughout the summer.
Chloroperlid, genus Alloperla.
(For a full discussion of the features used to ID Alloperla, see the entry posted on 5/26/12.)