Thursday, April 19, 2012

Spiny Crawlers (E. dorothea), Flatheaded Mayflies (Rhithrogena) and Much More at the Upper Doyles River

The rocks in mid-stream were covered with these little yellow stoneflies today.  Below is a photo taken on Sunday (4/15) of what appears to be the very same species that was sent to me by a friend (used with permission).

While neither one of us is an expert on stonefly adults -- we mainly work on identifying the nymphs -- based on similar photos by Tom Murray and others, our guess is that these are Chloroperlids (Green stoneflies), Sweltsa onkos (see, for example,  It was pleasant to be working with them as companions, while watching mayflies hatching as well.

The Upper Doyles is filled with insects at the moment -- well, that's true for a lot of our streams: lots of Rhithrogena flatheaded mayflies and spiny crawlers, all E. dorothea.  Let's take a look.

1.  The flatheaded mayfly, genus Rhithrogena.

A real beauty with the black wings of a nymph that's fully mature.  We'll let this nymph represent the possibly "hundreds" of these that I saw today.  I picked up one rock, not a very big rock, and counted 35 Rhithogena nymphs gathered together, side-by-side, in a space that was 2" X 3" -- and they just sat there looking at me!  I see this genus of flathead in very few streams, but it seems when I find them, I find them in very large numbers.  I reported the very same thing from the Lynch River on 3/29.  At the Lynch River these were joined by a lot of Diploperla Perlodid stoneflies, and I found the same thing today.

Diploperlas seem to have a "sweet tooth" for Rhithrogenas: the two Diploperlas in the photo above did in two of my Rhithrogenas before I quickly moved them into a bowl of their own!

2. Spiny crawlers: Ephemerella dorothea.

(Normal eyes on the first; large, red eyes on the second.  Is this a female/male difference as we found with the small minnow mayflies?)

I took a number of photos today with a new lens -- a "super" macro lens that magnifies from 1X -- 5X.
Here's a closer look at one of the spinys.

I also drew down on the abdominal segments to see if they had tubercles on them, taking this photo.

 It shows that they did not.  Lack of paired tubercles on the tergites -- tiny projections that stick out from the back of the tergite -- is one of the things that helps us ID these nymphs as E. dorothea.

I took one other photo with my new "super" lens for you to see.  I flopped my Rhithrogena nymph on its back and tried to get a good ventral view of the gills.  You'll recall that this is the flathead on which the gills form a complete oval.  I think you can see how the gills at the rear of the abdomen overlap.

When I get proficient at using this lens, I hope to use it more in my work.  It will allow me to photograph key anatomical features without using microscope photos of preserved insects.

One other thing from today.  I saw a lot of Isoperla holochlora Perlodid stoneflies that are more mature than the ones I've found so far this year: note how the rear edges of the wing pads are starting to bow.

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