Flatheads, Flatheads, Flatheads: A Trip to the Mechunk

I travelled out to Mechunk Creek this morning, hoping to find some dragons and damsels, but what I found was lots and lots of flatheads.   On some of the larger rocks that I flipped over, there must have been 10-15 nymphs running around.  There were all different sizes and all different colors -- almost all were Maccaffertium in terms of the genus.  In the photo above, the nymph on the left is a Stenacron nymph, that's a Maccaffertium on the right.  Here's a good look at one of the larger Maccaffertium nymphs that I found.

You may recall that these two genera are anatomically close in terms of gill structure: in both cases the gill on segment 7 is thin and fingerlike, not at all like the gills that precede it in terms of appearance.  But, Stenacron gills (gills 1-6) are pointed; Maccaffertium gills are truncated (sort of squared off).  Here are some microscope photos that make the point clear.

Stenacron:

Maccaffertium:

The Stenacron nymph in the picture above is clearly in its "pre-hatch" colorful stage, and it's worth looking back to a photo I took on March 18th at Whippoorwill Branch of younger Stenacron and Maccaffertium nymphs that I caught swimming together.

I can't say for certain that the dramatic change in color in the nymphs that I found today is entirely because of maturing -- a difference in species might be involved.  Still, an enrichment of color and pattern is something we've witnessed all year in mayfly and stonefly nymphs as they grow and mature.

What else did I find?  Well, there were some common netspinner caddisfly larvae and some fingernet larvae as well, I also saw a fair number of Brushlegged mayflies and a couple of Perlesta common stoneflies -- and this stream is loaded with snails (mostly Pleurocerids).  But I did find one dragonfly -- another Darner dragonfly (family: Aeshnidae).  It was a big one -- a little bit over an inch.

Finally, I'm starting to find small Hellgrammites.  But the one in the picture below is sort of a "teenager" when compared to the babies we'll start to see in July and August.  If you ever find one of these and are not really sure that it's a small Hellgrammite, just look for the four hooks that are attached to prolegs at the rear of the insect: they seal the deal.

Another look at the beautiful Stenacron flatheaded mayfly found in Mechunk Creek today.