Sunday, April 20, 2014

A new Perlid (common stonefly) at Entry Run? Acroneuria internata

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.

4. A "Northern case-maker" caddisfly larva, Pycnopsyche gentilis in its case made of stones.  Very nice case, and not the only one that I saw.

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?


  1. Large-Flowered Trillium, Trillium grandiflorum.
    Love your blog. Helped me identify Brachycentrus I found on Whitetop-Laurel last week.

    1. Thanks Doug -- for the information and for the comment.