Friday, November 8, 2013

Colorful stoneflies at the Lynch River

One new insect for the new season at the Lynch River this morning, but for the most part I saw the stoneflies we've been seeing in a regular way, just more mature and with greater color.  To wit, the beautiful Perlodid stonefly in the photo above, Clioperla clio.

And another Perlodid that we also see at the Doyles and at Buck Mt. Creek, Helopicus subvarians.

I was a little troubled by the leading edge of the dark transverse band on the head of this nymph.  Remember how Beaty describes this on H. subvarians: "anterior margin of dark, transverse ocellar band a straight line or mostly so."   H. bogaloosa, on the other hand, has a dark transverse band on which "two dark lobes project into anterior light area."  (Beaty, "The Plecoptera of North Carolina," p. 21)  But there was no question about the ID -- H. subvarians -- once I looked at the occipital ridge (back of the head).   Beaty's descriptions: H. bogaloosa -- "occipital spinules typically grouped into a single irregular row": H. subvarians -- "occipital spinules grouped into broad patch of 2-3 irregular rows."  (p. 21)  I see 2 rows on this one: Helopicus subvarians.

The third Perlodid I found was the new one -- well, is the one I saw for the first time this season: Diploperla duplicata.

When they're this size, they're not much to look at.  But come April...spectacular!


Small winter stoneflies -- I only saw two, but they were the biggest I've seen so far this season: 7 mm.

We need to see wing pads to identify small winters to the level of genus, and they're still hard to see in these live photos.  So, let's take a look with the microscope.

Genus, Allocapnia -- which is just about the only genus we see in our streams.  Remember Peckarsky's (Freshwater Macroinvertebrates, p. 66) description: "Metathoracic wingpads usually truncate, unnotched or notched on inner margin near tip....Allocapnia."  These are definitely notched.  Last winter I tried to get these down to the level of species ID.  But there's no sense in working on this until our nymphs are mature.

Mayflies -- Still seeing mostly flatheaded mayflies and brushlegged mayflies.  I again found a Maccaffertium vicarium, one of handful of Macs I can ID to the level of species.


Off to the Rivanna on Sunday where I'm quite sure I'll be seeing large winter stoneflies.

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