Sunday, September 4, 2011
Heptagenia marginalis -- Finally, One That's Fully Intact!
Our beautiful "summer" flatheaded mayfly -- Heptagenia marginalis -- and one with all of its legs and tails! If you've ever tried to pick up flatheaded mayflies with tweezers, you'll know that they start falling apart the minute you look at them! Off comes a leg -- or two -- or one of the tails is broken. So I was thrilled to finally get a photo of one of these beauties on which nothing is missing. I also found one that had just recently molted. Note the light color: it takes awhile for the pigment to darken. Black, oblique lines on the sides of the abdominal segments help us to ID this particular species. Pretty clear on this nymph.
Also note that the wing pads on both of these nymphs are starting to look pretty long. Since most guides say that Heptagenia marginalis usually hatches by the end of August or start of September, these two are a little behind!
I took a quick trip to the Rivanna River at Darden Towe park this morning in full knowledge that there, at least, I was bound to find moving water. I also had hopes of finding more Leptocerid cases (Long-horned case making caddisflies). But I didn't: they're very hard to see since they look like tiny bumps on branches. In fact, here too, as at Buck Mt. Creek, I didn't find a whole lot of insects. The summer netspinners are pretty well gone. I saw quite a few common stoneflies, mostly small, and a lot of hellgrammites -- small, large, and all sizes in-between. Then, too, there were quite a few flatheaded mayflies, most of them Maccaffertium in terms of the genus. I did bring a few of those home to see if I could work out the species ID.
I also found a couple of small minnow mayflies -- and I do mean a "couple". One was Acentrella nadineae, the other Baetis intercalaris. Pictures below. (Shouldn't these all be hatched by now?)
Still no sign of our "autumn" small minnow mayfly -- Acentrella turbida -- but I think it's still a little bit early for that nymph to show up. Below, another look at Heptagenia marginalis. May be the last one I see until next year at this time.