Sunday, September 23, 2012

Small Beginnings: The New Season Starts at the Rapidan River

There were two insects I was hoping to see at the Rapidan River this morning: I only found one -- the spiny crawler mayfly, Ephemerella subvaria.  (I did not find the Perlodid stonefly, Isogenoides hansoni -- maybe next time.)  Now, I could have cropped this photo for a closer view of the nymph -- but that wouldn't do justice to its actual size: 2 mm!  That's small.  By the time these nymphs mature in February and March -- creating the "Hendrickson" hatch -- they will be 8-12 mm, and look something like this (photo taken on 2/17 of this year).

But they really are small at the moment, and I'm pleased that my photos turned out as well as they did.


It was a morning for finding small insects -- as it should be, we're at the beginning of a new season.  Here are a few more insects that will mature over the winter and hatch next year in the spring.

1. A free living caddisfly larva, Rhyacophila fuscula. This was 1/2" long at the most; at maturity the larva will be well over an inch.

A mature one in the photo below.


2. Common stonefly, Paragnetina immarginata (I think...), like the E. subvaria mayfly, a taxon I only see in this stream.  I found a lot of them: here are photos of two.   (The clue to a P. immarginata ID, by the way, is the dark, longitudinal bars that run about 2/3 the length of the femora.)

The largest of these was about 1/2" in length: the mature nymph is 1 1/4 -- 1/12" long -- and much more colorful.


3. Giant stonefly, Pteronarcys biloba.

This is not the first time I've seen giant stoneflies this year, but this is the first nymph that I was big enough for me to ID at sight.  Still, this one was "small," a little over 1" in length.  At maturity P. biloba nymphs are close to 2 inches.  In one of the photos I took, you can see that little E. subvaria spiny crawler: this will give you some sense of how small it was.


4. A small Leuctrid stonefly, genus Leuctra.  I don't expect to see these much before winter.


Naturally, I did find some other insects that are still "hanging on" from the season that's now ending up.  These included this "humpless" case-making caddis (Brachycentrid) -- Brachycentrus appalachia:

And that little small minnow mayfly that is literally "hanging on" (!) is a still immature Baetis intercalaris.  Here's a much better photo.

Finally, there was another small minnow mayfly that, as you can see, is certainly ready to hatch: Plauditus dubius, male.


It was a spectacular, early fall morning in the Rapidan valley.  Lots of color -- blues, purples, oranges -- provided by the many flowering bushes.

No comments:

Post a Comment