Thursday, March 15, 2012

The Small Minnow Mayflies Take the Day at Buck Mt. Creek

They're the only small minnow mayflies I see in Buck Mt. Creek in the winter and early spring -- Heterocloeon amplum, and they turned out in large numbers today.  This one is almost ready to hatch -- black wing pads.  But I found them in a variety of sizes and shadings, making the point very well that "hatches" don't occur all at once: H. amplums probably mature and hatch in Buck Mt. Creek from the beginning of March, through April, and possibly into May.

Let's look at the range of development that I saw today, working backwards from the mature nymph in the photo above.

1. A male  -- note the large, red eyes -- that is fully colored, still the wing pads have not started to darken.

2. Holding on to the back of the mature nymph in the photo at the top of the page, another male.  But note the light coloration, and, note how the eyes seem to be part red and part black (!)  I've seen this before in "teen" males, so I guess their eyes change as they mature.

3. Finally, an immature nymph that is still very light in color.  For a moment, I thought this might be an early sighting of the small minnow species Baetis intercalaris -- which I expect to see soon in this stream -- but, only two tails on this one, and the faint tracheation in the gills confirms that it too is H. amplum.

Too bad there are no trout in this stream.  If there were, fishermen could look forward to two months of "Blue-winged Olive" fishing.

As for the rest of my findings today --

1. A real surprise -- a small winter stonefly!  This blew me away.  I was sure they were, by now, completely gone from our streams.  But, still a few late bloomers hanging around.

2. A spring insect that we find in this stream -- the "Net-winged midge," Blephariceridae, genus Blepharicera.  This is a very intolerant insect with a TV or 0.0.  Still, I normally find them -- as I did this morning -- crawling on rocks on which there are large clumps of black fly larvae.  Go figure.  Below, dorsal and ventral views.  Note the "suckers" on the ventral side which they use to cling to the rocks.

3. One of many Perlodid stoneflies, Isoperla namata.  (Two sources confirm the existence of I. namata in Virginia, so I'm dispensing with the tentative Isoperla nr. namata.)  They're showing up in large numbers in this stream as well.

4. And finally, the Perlodid stonefly that I see in this stream in a regular way throughout the winter -- Helopicus subvarians.

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