Saturday, October 8, 2011

Still Summer in the Rivanna at Crofton

(To fully enjoy all of the photos in this blog, click on them twice to enlarge them.)

I thought it was time to get back to our "big" river -- the Rivanna -- to see what I might find there in early autum, and my favorite place to go on the Rivanna is below the bridge at Crofton.  Lots of small flatheaded mayflies, a few fingernet caddisflies (very few netspinners -- which was surprising), a few common stoneflies (genus Acroneuria), and a lot of narrow-winged damselflies (Coenagrionidae).  But I also found the treasure in the photo above -- a "Long-horned case-maker caddis": Leptoceridae, genus Nectopsyche.

Regular readers will recall that I found one on 7/13 in the Rivanna at Milton, and I've discussed Leptocerids in some detail in the entry posted on 1/26.  But it's difficult to overstress just how small these case-makers are and how difficult they are to find -- especially when you're looking for them in the way that I do.  I'm not taking a sample with a net, I'm  lifting up rocks that are covered with stringy, green vegetation and looking for one strand (the "needle in the haystack) that might be a little bit wider at the top than all of the rest.  It's tough, and pretty much happens by chance.

In these photos you can see how the case is attached to three slender stems.  The entire assemblage measured 16mm; the case itself was 1mm wide!  So, I wish my pictures were in better focus, but this is about as well as I could do.

For close-ups, I have to resort to microscope shots, and the two I've posted below are "file photos" -- these are not shots of the larva that I found today.  Still, it's the same genus, and this is what this caddis looks like close-up and then out of its case.

Note that the "hind" legs are the longest of the three pairs of legs, and it's always those that you see sticking out of the case.  (For more on the name -- "long horned" -- see the posting of 1/26).

As I mentioned, I also a lot of narrow-winged damselflies, probably the most that I've ever seen at any one time.  Some were fairly mature -- a lot were not, they were small.  (Could these be offspring from damsels that hatched earlier this year?)   But here are shots of two of the big ones.

Pretty nice.  But we should end with a view of our long-horned caddis -- he was in the process of crawling across my tray.

I'm not sure there's anything more exciting in doing this business than putting a little case like this into the water, watching it, and all of a sudden seeing it move.  Only then do you know that "somebody's home"!

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