Friday, May 11, 2012
Holy holochlora! Isoperla holochlora Nymphs Take Over Powells Creek
What else can I say? They were all over the place -- well, mainly in leaf packs. Still lots of E. dorothea spiny crawlers in this stream as well, but I think the I. holochlora Perlodids had it today in terms of sheer numbers.
No objection from me. This is one of my favorites of the Perlodids, and with a tolerance value of 0.7, it's a fair indication that we're looking at a pretty good stream. Some more photos.
Once again I went to the Powells looking for small minnow mayflies and a Neoperla common stonefly.
No Neoperla, but I did find a number of small minnow mayflies -- and they were small! I found one Acentrella turbida and two of the following -- which I thought would turn out to be Baetis intercalaris.
As soon as I uploaded my photos, I knew I was wrong. No pale parentheses marks () on the abdominal segments, and the middle tail is too short. This is actually a very young Baetis pluto, and one day it will look something like this.
I know that's hard to believe, but we can already see the key characteristics of the B. pluto species: 1) the "middle caudal filament [=tail] is 3/4 to subequal to lateral filaments, usually with distinct dark band on caudal filaments medially" (Steven Beaty, "The Ephemeroptera of North Carolina," p. 6). And 2) "tergum 5 [is] relatively pale" (same source). Have a look.
The way these nymphs change -- in color and pattern -- as they mature is simply remarkable. Still, I was surprised to see one so small at this time of year. One year ago today (5/11/11) I found the following B. pluto nymph in the very same stream (note that the middle tail is broken off).
A couple more shots of our nymph.
One more interesting insect from Powells Creek today. It's a Glossossomatid caddis larva -- a "Saddle-case-maker" -- a case-maker I associate with the winter. I'll need to adjust my thinking! Three good photos. The first is a dorsal view of the case; the second is a ventral view of the case with the Glosso tucked inside (head at one end, anal prolegs sticking out at the other); and in the third photo, the larva was crawling out of its case. Unlike most case-makers, the Glossossomatid does not hesitate to abandon its case when it's disturbed.
And we close with a photo that pretty well sums up the day.