Saturday, April 2, 2011
Buck Mt. Creek: Perlodid stonefly -- genus Helopicus
Another week, another new Perlodid stonefly genus -- or so it seems. This is genus Helopicus, and this is the first time I've seen it (well, the first time I've known that I've seen it!)
It was a sunny day when I set out for Buck Mt. Creek. But as soon as I found some insects for photos it clouded up, and I thought the day was a loss. I had found lots of small minnow mayflies, a few small spiny crawlers, an Epeorus flatheaded mayfly, and lots of very big black flies. The clouds made it impossible to get any good shots.
So I headed back to the car. But there was a riffle on the way back to the car in which I had found lots of insects before, so I decided -- if the sun comes out, I'll stop and see what I can find. The sun came out -- and I found the same insects I had found in the first riffle, some "Net-winged midges" mixed in with the black flies -- but, three beautiful stoneflies. As I took some photos, I realized these were Perlodid stoneflies, not "common stoneflies" (Perlids), and that this was a genus I had not seen before. So I preserved a few and headed home to my lab.
When I keyed this out, I came to a choice between the genera Yugus or Diura. This was based on the fact that there is a "knob" below the second lacinial tooth. (In the photo below, the nymph is turned on its side, and this is the underside of the head. Laciniae are part of the maxillae -- jaws.)
But, Diura is not a genus that is found in Virginia, and I had found a Yugus last week, and this nymph did not accord with the morphological features that are found in that genus (see Stewart and Stark, Nymphs of North American Stonefly Genera (Plecoptera), p. 455). Below -- Perlodid stonefly, genus Yugus -- note the completely different pattern on the head.)
When I looked at pictures of Perlodid stoneflies on "Bugguide.net," the only thing I saw that resembled the nymph I had found was genus Helopicus -- a Perlodid stonefly with a "head with a transverse brown band between [the] antennae" (Steward and Stark, p. 397.) But, all the keys say that Helopicus Perlodid stoneflies have "submental gills."
Back to the microscope. When I lifted the head and looked carefully below the chin at the top of the neck -- sure enough, there were submental gills, fingerlike projections that stick out from the submentum that are "twice as long as the greatest width" (Peckarsky, et.al., Freshwater Macroinvertebrates of Northeastern North America, p. 71.)
I had found what for me was a new genus of Perlodid stonefly: the gills, along with the "dark transverse band between the eyes" (Peckarsky, p. 71) give us Helopicus. Another look at this beautiful creature. (Should we think of it as the "Lone Ranger" of Perlodid stoneflies?! Sure looks to me like it's wearing a mask.)
This is exciting: I love finding new things. I worry about what I will do when there are no new genera to find (may never happen). Then I'd have to move west to find the variety that I've come to enjoy!