Sunday, November 2, 2014

Small beginnings: winter/spring insects at the Rapidan River

A challenging day for photography.  It was cold -- 46º -- and extremely windy (= watering eyes).  But the real challenge was the sun -- which kept popping in and out of fast moving clouds.  But I still did alright.

I continued to see strong-case makers (Odontoceridae) and humpless case-makers (Brachycentridae) -- but not nearly as many as I saw here last month (10/5).  Rather, the small mayflies and stoneflies that will mature in the spring are suddenly here in big numbers.  I left the pronggilled mayflies alone, choosing to focus instead on...

1.  The spiny crawler mayfly, Ephemerella subvaria (in the picture at the top of the page).  Dozens and dozens of them in the leaf packs, and you can see them at once because of their colors.  The tibial banding, by the way is a key for identification.

They'll be hatching in March and April, and when mature they look more like this.


2. Perlodid stonefly, Isoperla montana/kirchneri.  First of the season.

Very, very small: I'm pleased that this turned out as well as it did.  Given the size -- about 3 mm -- I should hesitate on the ID,  but I feel pretty confident.  Look at one that's fairly mature.

There are commonly two dark bars at the back of the head, and the abdomen's striped with the middle stripe formed by a series of crosses (or a line with dots on either side).  That middle stripe was already clear in a microscope view, and you can actually see the dark bars at the back of the head on this tiny nymph.


3.  Another small Isoperla -- about 7 mm -- which turned out to be I. similis.

These mature rather quickly.  I found this one in February last year.

The head pattern is distinctive: "head brown with a pair of pale spots near labral suture, a pale M-shaped mark anterior to median ocellus and pale marks anterolateral to the lateral ocelli."  (Beaty, "The Plecoptera of North Carolina," p. 24)  Difficult to see the "pale spots near the labral suture" on this young nymph.  But you can see them if you look closely.


3. Common stonefly, Paragnetina immarginata.

So much nicer when we find them in July.  Spectacular, really.

Still, we can already see a lot of key features.  "M-pattern with medial pale line extended anteriorly, often connected to pale frontoclypeal margin; yellow femora distinctively patterned with dark brown longitudinal bar extending about 2/3 the length; abdominal terga banded, anterior half dark; anal gills absent." (Beaty, p. 18) All Paragnetina nymphs have a complete setal row on the occipital ridge (back of the head).


4. And I saw a number of, not so small, flatheaded mayflies, Maccaffertium pudicum.

When mature, this is one of the biggest Maccaffertiums that we see: 11-14 mm.

Such a pleasure to go to a stream where there are so many insects to see.

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