Sunday, October 20, 2013
One by one the new Perlodids appear: Helopicus subvarians and Clioperla clio
There are days in this business when you find exactly what you're expecting to find, and today was one of those days. This morning when I drove out to Buck Mt. Creek, I thought it likely that I'd start to see the Perlodid stoneflies Helopicus subvarians and Clioperla clio -- and I did. Of course, both insects were still very small: the Helopicus nymph in the picture above was -- I'd guess -- about 10 mm in length; the Clioperla was smaller, maybe 6 or 7 mm.
Helopicus nymphs are easy to spot by their colors and the pattern we find on their heads -- "frons with a complete dark transverse band through [the] ocellar triangle." (Beaty, "The Plecoptera of North Carolina," p. 21) On H. subvarians nymphs, the leading edge of this band is a "straight line or nearly so." (Beaty, p. 21) While there is a slight "dip" in the anterior edge of the band on this small nymph, we will not see that on the more mature nymphs later on in the winter -- like this one from 2/6 of this year also found at Buck Mt. Creek.
C. clio nymphs, on the other hand, are not so easy to distinguish when they're small like the one that I discovered this morning.
Not much to go on.
Still, one of the key features for the species ID can be detected -- the "large light area on [the] dorsum of [the] head." (Beaty, "The Plecoptera of North Carolina," p. 20)
That large, light area really stands out when the nymphs color up as they mature.
Two other nice insects this morning at Buck Mt. Creek.
1. Giant stonefly, Pteronarcys dorsata (corners of pronotum are "produced," and no projections on the abdominal segments).
2. And a beautiful common stonefly, Acroneuria carolinensis.
The tergites are banded: "anterior half light and posterior margin of tergites dark." (Beaty, "The Plecoptera of North Carolina, p. 14) The reverse is true of the more "common" common that we've been seeing, Acroneuria abnormis.
Perlodid stonefly, Helopicus subvarians....