Sunday, May 1, 2011

Stream Report: Back to Buck Mt. Creek

So, what's your guess?  You need a close-up you say?  Glad to oblige: here's a microscope view.

Any ideas?  An alien from outer space?!  Actually, this is the pupa of a Net-winged Midge, and it is one wierd-looking critter.  When Rose and I saw one of these in the lab, we had no idea where to begin in terms of "keying" it out; we didn't even know what "order" to start with.  Fortunately our learned Director, John Murphy, had seen these before and knew what it was.  He sent us to p. 171 in Voshell (A Guide to Common Freshwater Invertebrates of North America), and right there it was.  There are a lot of these at the moment in Buck Mt. Creek, securely attached to the rocks.  But, there are still larvae around, so I was able to get a side-by-side pic of a larva and pupa.

I returned to Buck Mt. Creek to look for more Rhithrogenas (genus of flatheaded mayfly), and I did indeed find them: some pretty big, some pretty small.  This is not the only flatheaded genus I found.  I also found one Epeorus and one Leucrocuta.  I got a decent shot of the latter.

But on Rhithrogena -- what I hoped to get with my camera was a good look at the large, "suction cup" gills that form a complete oval on the underside of the nymph.  It can't be done.  The reason -- they're actually transparent and only show up with the contrast you can get in a microscope view.  So, here's a dorsal, live view of our insect, followed by a microscope view of the ventral side showing the gills.  It should be clear from this photo that the gills do indeed form a full loop.  (Note:  The "frilly" hairs that stick out on either side of the abdomen are not the gills.  This is "fibrilliform" that is either on top of the gills or -- more likely -- underneath: I have to check.)

Dorsal, live:

Ventral (abdomen only), microscope view:

Pretty neat!  I found two other things of interest.  The first is that, as I did last time, I found some tiny small minnow mayflies, and this time I did get live photos.  Let me show you two different nymphs.

I was quite happy: finally, some live pix of Heterocloeon nymphs (the genus I found last week).  I kept both nymphs so I could verify the genus at home -- I'm afraid I was disappointed!    These are not Heterocloeon -- there is no "large pigemented area" in the center of the gills; the gills are veined.  So, they're either genus Baetis or genus Acentrella (the other "two-tailed" genera) -- I just couldn't tell.   The difference between them?  Baetis nymphs have metathoracic wing pads; Acentrella nymphs do not.  I'll check back in a few weeks to look for bigger specimens -- these were very, very small.

My final point -- the taxon of the day was clearly the spiny crawler mayfly.  They were all over the place in every size and color  (all genus Ephemerella).  Here's a photo of two that lined up side-by-side in my dish.

I've noted before, that spiny crawlers like to live in the moss that grows on the rocks.  But, there were no such rocks in the riffles I sampled.  So, where did I find them?  Some were simply crawling around on the bottoms of rocks, but most were in leaf packs!   One wad of leaves and twigs that I pulled out of the water was literally crawling with them.  Two photos follow.  The first is a pic of the ball of leaves; in the second -- a close-up -- you can clearly see two of the resident nymphs.  (Click on the photo to enlarge the image.)

Of course there were other things in the stream.  I found water pennies, common netspinners, fingernet caddisflies (genus Chimarra), one Nemourid stonefly (genus Amphinemura), and a number of Isoperla Perlodids.  In fact, let me close with a photo of a Rhithrogena flathead and an Isoperla Perlodid that moved together and posed.

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