Friday, March 4, 2011

"Hidden Streams" and the Quality Insects they Hold

(A "group shot" of a Giant stonefly with a freeliving caddisfly and a green stonefly (Chloroperlid) between its left legs: it's resting its head on the case of a Lepidostomatid caddis [inhabited].)

Today's stream must go unnamed: it's on private land -- but I did have permission to explore it.  It's a high elevation tributary to the Moormans River.  The land is totally forested, and the stream tumbles down a steep, rocky ravine: the water is crystal clear.  And the insects I found are the kind of insects you'd expect to find in a stream of this sort.

1. Stoneflies.  Eight stonefly families were represented in the nymphs that I found: Roach-like stoneflies (Peltoperlidae); Nemourid stoneflies (genus Nemoura); small winter stoneflies; large winter stoneflies (genus Strophopteryx); Giant stoneflies (lots of them); common stoneflies (Perlidae), both genus Acroneuria and genus Eccoptura; Perlodid stoneflies -- Isoperla and Diploperla; and green stoneflies (Chloroperlidae), genus Sweltsa.  Stunning!  The only family I didn't find was Leuctridae (rolled-winged stoneflies).  I have no doubt that I'll see them here later on in the spring.

II. Mayflies.  Only three families -- Heptageniidae (flatheaded mayflies), Ameletidae (Ameletids) and Leptophlebiidae (pronggilled mayflies).   But, as we know, Ameletid mayflies and pronggilled mayflies are only found in very good water, and there were three different genera of flatheads represented: Epeorus (lots of them -- but then it's their season), Maccaffertium, and Leucrocuta.   Again, having multiple genera of flatheads present simultaneously in a stream is, I think, a sign of a very good stream.   (I will have to revise what I said in my entry on "Flatheaded Mayflies" -- 1/8/11-- on the genus Leucrocuta being around mostly in "summer".)

III. Caddisflies.  Many rocks were simply covered with Uenoid cases -- all of them occupied, and I found a couple of Lepidostomatids.    I also found several freeliving caddisfly larvae and a lot of common netspinners, all of the netspinners genus Diplectrona -- which I noted in my entry on common netspinners (1/5/11) has a very low tolerance value.   Note the color, sort of grayish brown, not the "green" we've come to expect with our netspinner friends.

There are two things we look for when we identify this particular genus.  1) It has a "simple" fore trochantin (i.e. not a "forked fore trochantin as we find with the common genera Hydropsyche and Cheumatopsyche).  It's just barely clear in this picture.

And 2), the "meso- and meta-notum [are] divided by a transverse fracture line in the posterior third" (Peckarsky,, Freshwater Macroinvertebrates, p. 101).  Those lines are very clear in this photo.

On the "freeliving" caddisflies -- I've already written about the problem of color (see "The 'Other' Freeliving Caddisfly," ): most people think they're always dark green, and they're not.  In that previous entry I had photos of one that was brownish gray.  Today, I found two additional colors: one was a kind of light, aqua green; the other was a creamy tan.  Here are the photos (and I apolgize for the poor quality of the first).

(Note that the back edge of the pronotum, on both larva, forms a black collar in the shape of an inverted "U".)  When I had this second caddisfly in the tray to take its photo, it was conversing with a green stonefly: I'm not sure the green stonefly realized that freeliving larvae are predaceous!

Some things you just learn the hard way!

4. Photos.  I'll finish with a few photos, since there were so many good pictures to take.

1) A Giant stonefly in the tray in full sunshine.

2) A Giant stonefly that did the "backstroke" for us to show off the tufts of gills that cover its thorax.

3) A lovely Perlodid stonefly, genus Diploperla.  (Later note: This is not Diploperla -- looks like Isoperla, probably Isoperla similis.  9/25/11)

4) And a Perlid stonefly (common), genus Eccoptura.  Note the distinct reverse "T" shape in yellow on the front of its head.

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