Thursday, November 14, 2013
Not much action, but some beautiful insects at the Rivanna at Crofton
This morning I decided to go where I knew there'd be water -- the Rivanna River at Crofton. I didn't see a lot in the insect department: common stoneflies (A. abnormis and A. annulipes), Giant stoneflies (Pteronarcys dorsata), and a number of large winter stoneflies (genus Taeniopteryx). Pretty much the same collection I saw at Darden Towe Park. But I found a couple of beautiful stoneflies, so I focussed my efforts on getting good photos.
1. Pteronarcys dorsata -- pictured above. Size was 22 mm, and note that it's fairly mature (the spread of the wing pads). But look at those beautiful colors. Beaty describes the common markings: "each tergite with anterior and posterior abdominal spots sometimes confluent to give the abdomen a longitudinally striped appearance (3-5 stripes possible)". (Beaty, "The Plecoptera of North Carolina," p. 28.) I see 4 rows of spots on the abdomen of this particular nymph. But as you can see, the spots that form the 2, more distinct lateral stripes actually start on the leading edge of the pronotum!
It's a real beauty.
And I got a great shot of the gills: Beaty -- "branched gills present on thoracic sterna and on abdominal sternites 1 and 2." (p. 28)
2. And then there was this magnificent common stonefly, Acroneuria abnormis (14 mm).
Beaty, you may recall, distinguishes two types of A. abnormis nymphs -- one with a distinct "M" pattern on the head (sometimes interrupted) and abdominal banding, and one that is lacking the "M," and is also lacking the abdominal banding, having terga that are "uniformly brown." (Beaty, "Plecoptera," p. 14.) I'd have to say this one is a bit of a mix. There is a light colored "M" on the head, albeit "interrupted," but the abdomen is totally brown.
Saw a number of large winter stoneflies but took only one photo.