There are nine stonefly families that inhabit our streams. I've talked about four of them in previous entries -- common stoneflies, Perlodids, large winters and small winters -- all of which can be found in a lot of our streams during the winter (now!). One of the other families is "seasonal," and shows up mainly in the spring, and it shows up in large numbers throughout the watershed. That's the Nemourid stonefly, and I'll say more about it at the appropriate time.
The other four families are rarely seen by folks who sample our streams, mainly because people don't know when and where to find them. The four stoneflies in question? "Roach-like" stoneflies (family: Peltoperlidae) -- pictured above; "Giant" stoneflies (family: Pteronarcyidae); "Green" stoneflies (family: Chloroperlidae); and "Rolled-winged" stoneflies (family: Leuctridae).
Roach-like Stoneflies (Peltoperlidae): (Photo at the top of the page.)There is no need to run to your microscope to identify this one: the wide head, wide body, short tails, and burnt orange color tell you all there is to know. There is no other stonefly that looks like this one -- not even remotely. We ought to know right away what they are, but I've sampled with volunteers who at first are convinced that they must be terrestrial bugs!
The Peltoperlids have a one year life cycle: they hatch as terrestrial insects in the summer -- May-August (high point in June). Thus we see small ones by the end of the summer and large ones through the fall winter and spring. (Photo of a "baby" Pelto below.)
They have a "tolerance value" of 2, so you might think that we'd see them in many places throughout our watershed, but that does not turn out to be true. I have only seen them, to date, in three locations: the StreamWatch reference site for Albemarle County, the Doyles River at the National Park boundary, and in a clean, small, high elevation stream in Byrom Park. But when we do see them, we often see them in very large numbers -- perhaps 50-60 in a sample of 200 bugs. And, they seem to love leaf packs. I've picked apart leaf packs and had Peltoperlids scatter all over the place -- it's like they were having a "Pelto party"! (Sorry.) Finally, they are fast moving critters. When you open a net with them on it, you'd better be ready for some quick work with the tweezers.
Giant Stoneflies (Pteronarcyidae): (Live photo above; actual size is about 1 1/2".) This is another nymph that should be a no-brainer when it comes to identification. It's almost always uniformly dark brown to black* (pattern isn't obvious), primitive looking, very short tails, and looks like it's wearing a suit of armor. If there is any question about identification, flip the nymph on its back and look at its chest: the chest of the Giant is covered with clusters of gills.
This stonefly also typically hatches in May-August. But it's "semi-voltine," i.e. it has a two-year life cycle, so we can see various sizes at various times of the year. Still, I've found only small ones (1/4 - 1/2" long) during the summer, and I find the large nymphs (up to 2"!) during late fall and early winter. Where do we find them? We see them at the Albemarle County reference site used by StreamWatch, at the Doyles River at the National Park, in Buck Mt. Creek, and, perhaps surprisingly, in many main stem locations in the Rivanna River. StreamWatch samplers working at Darden Towe Park in C'ville can almost be certain to see some in the summer and fall. (Below, mature nymph, March, 2010, secret stream).
To my knowledge, the Giant hatch is not that important to fly fishermen in the East: quite the opposite is the case in the West. Fly fishermen from all over the country converge on Montana and Oregon and other states in the Rockies in May and June for the infamous "Salmon Fly" hatch -- Pteronarcys californica. This is a BIG bug, and it brings the BIG Trout to the surface: lots of protein in just one bite!
Green Stoneflies (Chloroperlidae): Green stoneflies are not easy to identify on location. They can easily be confused with two other stoneflies -- "Rolled-winged" stoneflies (more on those below), and small winter stoneflies. All three are small (mature nymphs range from 1/4" - 1/2" in length), and before they reach hatching colors, all three are yellow. If the wingpads are fully developed the three can be distinguished using a loupe (assuming you know what you're looking for); otherwise, it's best to identify these in a lab. The Green stonefly does have one quite visible distinctive feature: the tails tend to be very short (actually, the tails on the nymph in the photo above are abnormally long).
Green stones normally hatch in July and August, so we often see mature nymphs in the spring. However, these stoneflies are also "semi-voltine," so there are nymphs of varying sizes in the streams all year round. Most of the Greens that I see, I see in the spring and the fall.
This is a stonefly that likes small, clean, mountain streams, so once again the StreamWatch reference sites are good places to go if you want to see them -- including the site in Fluvanna. We also find them in the upper Doyles River, Buck Mt. Creek, Long Island Creek (in Fluvanna), and the Moormans River.
We have two genera of Greens that we see. The one in the photo above is genus Haploperla; the one in the photo below is genus Sweltsa. One of the features that distinguishes these two genera is the angle of the wingpads in respect to the body: Haploperla wingpads (the inner edge) run parallel to the abdomen line; Sweltsa wingpads angle away from the abdomen line.
Rolled-winged Stoneflies (Leuctridae):
This little beauty is in full hatching colors, with the strong contrast of lower and upper body (we often see the colors reversed, by the way; i.e. the abdomen's yellow, the wingpads dark brown). You can see that when this nymph is fully mature, the wingpads are quite different than those of the Green stonefly.
But they're not too different from those of the small winter stonefly (in both cases, the primary wingpads are long and finger-like, the second set is short and stubby). Therefore, this is a stonefly that it's best to preserve and work out the ID in a lab.
Rolled-winged stoneflies hatch late: August through November. So we normally see them in the summer through early fall. Like the Green stonefly, the Rolled-winged stone prefers a "mountain stream" habitat -- streams that are small, cold, and clean (they have a tolerance value of 1). I have seen them only at the StreamWatch reference sites and the upper Doyles River. Nonetheless, the StreamWatch data indicates findings in Long Island Creek, the Lynch River, and Raccoon Creek as well.
* I was wrong about this. Some are richly patterned. See the pictures below for "The Rapidan River off of Graves Mills Rd." and "Hidden Streams."