Thursday, March 1, 2012
Spiny Crawlers: The Spring "Invasion" Begins
On to the "Spinys" in just a moment. But first, my "pic" of the day: a Northern Case-maker caddis (genus Pycnopsyche) in its usual three-sided case made out of leaves. Resting atop it -- an Ameletid mayfly and a Lepidostomatid caddis, who has not yet poked its head outside of its case!
And now --
They are here in force: Spiny Crawler mayflies (family, Ephemerellidae), and this is the common species we see in all of our streams in the spring -- Ephemerella dorothea (though, a word of caution on making that call in a moment). This was the dominant taxon among the insects I collected this morning, and this in a little stream in Sugar Hollow where on my last visit I saw more Isoperla nr. namata Perlodid stoneflies than anything else (today, I only saw two or three). None of the spiny nymphs that I saw today was very big, and some were very, very small. For example, here are two side-by-side: the one on the right is clearly quite immature.
In March and April -- perhaps into May -- I'll probably see more spiny crawlers than any other taxon in my trips to the streams. When it's their turn to move into the scene, they really take over the streams!
For fly fishermen, these provide good fishing in May and June as the Pale Evening Duns.
Not all of the Ephemerella nymphs in our streams are E. dorothea, and this is something I need to look into with care. In reading Beaty's discussion of this particular genus ("The Ephemeroptera of North Carolina," pp. 26-28), I now see that E. dorothea and E. invaria nymphs, when they're immature, are difficult to tell apart: they look much the same. When mature, E. invaria nymphs have paired "tubercles" (little projections on the posterior edges of abdominal tergites); mature E. dorotheas have none.
But, those tubercles might not be visible on immature E. invaria nymphs!
I have reason to believe that a few of the nymphs that I've seen this year were in fact E. invaria nymphs.
Especially this one, found in the Doyles River on February the 6th.
Note how this differs from the nymphs I was finding this morning. The leading edge of the pronotum is dark, and the femorae (first leg segments) are light in color without any banding. There is also what could be a dark "V" beginning to form at the top of the thorax. These features are in accord with the E. invaria nymph illustrated on p. 204 in Knopp and Cormier's Mayflies. And, the nymph in this photo looks exactly like an E. invaria nymph posted to Bugguide.net by Tom Murray (http://bugguide.net/node/view/267129/bgimage). So, I will be on my guard this spring and check my spiny crawlers with greater care than I have in the past. Still, I'm fairly certain that it's E. dorothea that we'll be seeing in the large numbers.
1. I found another "Rolled-winged" stonefly in this little stream, genus Leuctra, and this one posed for some nice photos.
2. I found several Ameletid mayflies, and the wing pads are starting to lengthen.
3. I found, for the very first time, a small minnow mayfly in a stream that is clearly "pristine." No surprise that it was Baetis tricaudatus.
4. And the "beauties" of the day were a couple of Green stoneflies (Chloroperlids), genus Sweltsa. These intolerant stoneflies are more colorful now every week.
(Below: another look at our Pycnopsyche. It came close to crawling out of its case, something I've not seen before.)