Saturday, April 6, 2013
Work to Do: New Species from a Small Mountain Stream
We went to a small stream this morning in the hills of Sugar Hollow, and I found two insects that I'm quite sure I've not seen before. The first -- this flatheaded mayfly, genus Leucrocuta. Leucrocuta, you'll recall, is a very small mayfly with a very wide head, one that we distinguish from Heptagenia flatheads by noting its lack of "fibrilliform" on gill 7.
Heptagenia has it; Leucrocuta does not. Another photo.
With the right key, I'm sure we could ID this to the level of species. Several features stand out as unique: 1) the head is much wider than it is deep; 2) there are very few pale markings on the femora; and 3) each tergite has a pair of pale markings. But I've not yet found a key that will take me to species level ID. Beaty tells us to "leave at genus" with Leucrocuta ("The Ephemeroptera of North Carolina," p. 19). I can make a guess: Leucrocuta juno -- the "Little pale evening dun." But that's an ID that's based on Donald Chandler's photo of a nymph of that species (http://www.discoverlife.org/mp/20q?search=Leucrocuta+juno).
I found two other Leucrocutas (actually, I saw a lot of Leucrocutas) this morning that were clearly some other species. Unfortunately my sample photo is a poor one.
Even so, this is a species I have seen before. In fact I found it last year in this very stream on 5/1.
This species has a very distinct lime green area on the first abdominal segment, and very distinct pale areas on tergites 7 and 8. This is a species that I commonly see in our small mountain streams -- but here, too, I don't know the species ID. Could be L. aphrodite. So, more work to be done on these Leucrocutas. I hope that Steven Beaty can point me to a useful source of information.
The other new insect that I found this morning was this Rhyacophilid -- free living caddisfly larva.
I don't think I've seen this before.
I have seen similar Rhyacophilids: R. nigrita and R. glaberrima. They look like this:
But they're not quite the same. The pronotum of R. nigrita has that distinctly dark leading edge, while the head of R. glaberrima seems to be richly patterned.
For this one I do have a key I can use -- Prather and Morse, "Eastern Nearctic Rhyacophila Species, with Revision of the Rhyacophila invaria Group" (Transactions of the American Entomological Society, 127 (1), 2001, pp. 85-162. So, off to work I go. If I figure it out, I'll let you know.
And there was more...
1. The Nemourid stonefly, genus Amphinemura. This was a small one -- 4 mm.
This is the Nemourid we commonly see in the spring -- sometimes in large numbers -- so I've been expecting to see it, but I expect to see it in bigger streams: Buck Mt. Creek, Powells Creek, Mechunk Creek, etc. I had to check Beaty on this one ("The Plecoptera of North Carolina," p. 3), and that cleared things up: "Habitat: In both small, headwater streams and larger streams and rivers (may be species specific)." Note the frilly gills at the neck (cervical gills). Those gills tell us the genus.
2. Flatheaded mayflies, Maccaffertium merririvulanum. I photographed two: the second is much further along in development (notice the length of the wing pads).
3. Spiny crawlers, Ephemerella dorothea. Boy, were they ever small (~ 5 mm)! But then, this was a small stream, high elevation, very cold water: things are bound to be further behind.
4. And I saw a bunch of Limnephilids (Northern case-makers), Pycnopsyche gentilis. No three-sided cases made out of leaves: these all had substantial cases with pebbles cemented together.
Here's the stream we were working this morning: small and shallow.