Saturday, December 3, 2011

A "Show Stopper" in Sugar Hollow: An "Adult" Small Winter Stonefly

My headline today was going to be "Everything But Small Winter Stoneflies," and then this nymph started to flutter its wings just as I was getting ready to take its photo!  It's a small winter stonefly -- here perched on a Green stonefly -- and the first adult that I've seen this season.  And it was a "show stopper" -- no question about it.  More photos:

and one in profile,

Note how they fold their wings flat on their backs when not in motion.  Pretty spectacular, on a day when I thought I hadn't seen any small winters at all!

But there was another discovery -- not made until I came home and downloaded my pictures.

My intent was to get a shot of the Perlodid stone on the right -- which turned out to be Isoperla similis (TV of 0.8) -- and I totally missed the nymph on the left: it's a very tiny Leuctrid, a "Rolled-winged" stonefly.  It will look like this in 3-4 months.

While the I. similis nymph will look something like this (both of these photos were taken on March 16th of this year.)

Let me spend a moment on the Leuctridae family.  This is a stonefly we see in very few streams.  They like small streams and very clean streams (this is probably genus Leuctra, which has a TV of 1.5).  This can be confused with a small winter stonefly:  the abdomens have a similar shape -- long and cylindrical.
But there are two ways to tell them apart.  First, look at the wing pads of the Leuctrid in the photo above.  The front wing pads are longer than the rear wing pads -- as with the Allocapnia small winter stonefly.  But remember, the rear wing pads on the small winter stonefly are wide and flat; on the Leuctrid the rear wing pads are about the same width of those in front.   The wing pads on the nymph that I found this morning are very hard to see.  But here is a microscope view.

Compare those to the small winter wing pads.

The other way to distinguish the nymphs of these two different families (Leuctridae and Capniidae) is to look at the "ventrolateral folds" on the abdomens.   These can be picked up as a color change on the edges of the abominal segments.  On Capniids (small winters), there are ventrolateral folds on segments 1-9; on Leuctrids, they only show up on segments 1-4.

small winter ventrolateral folds:

Leuctrid ventrolateral folds (I can only make out those on segments 1-3 on this tiny nymph).

I was very happy to find a Leuctrid this early since now we can watch them develop and change through the winter.  The streams where I find them?  The small mountain tributaries that flow into the Moormans.   These are streams from which I have trouble staying away.

Despite the fact that the sun kept moving on me (!), I managed some very nice photos today, so I'll simply run through them.

1. A nice, fat crane fly larva -- genus Hexatoma.  This is the one with the big bulbous end that swells up when the larva's preserved.  (The "common" crane fly larva we see is genus Tipula.)

2.  A fairly large (already!) green midge (Chironomid), and that's a Chloroperlid stonefly next to it on the right.

3. A lovely common stonefly -- Eccoptura xanthenses.

4. And a couple of Peltoperlids (Roach-like stoneflies): the dark one looks to be genus Tallaperla; the light one (freshly molted) has the beginnings of the marks on its mesothorax that would make it Peltoperla).

The dominant taxa today were: 1) Peltoperlids -- I saw hundreds of them in the leaf packs; 2) Crane fly larvae -- all over the place; and 3) Giant stoneflies.  There were also a fair number of Chloroperlids (Green stoneflies), and a few tiny pronggilled mayflies -- but only the one small winter stonefly!

1 comment:

  1. I thoroughly enjoy being able to see the great detail in your photographs.