Thursday, March 31, 2011
Stoneflies: Pictures of How They Change, Pt. II. -- Large Winters
(Large winter stonefly adults: North Fork of the Moormans, April 12, 2010.)
This is the last entry I'll post in this series -- showing photos that illustrate how nymphs change as they grow and mature -- it is also the last "new"material I'll add to the blog for a week -- I'll be on a mini-vacation next week. For new entries, please check back next weekend -- April 9-10.
Our focus here is the large winter stonefly, genus Strophopteryx. The changes you'll see in this sequence of photos pretty much follow the track that we've seen -- as the nymphs mature, they become darker in color, the patterns enriched, and the wingpads get longer. There is one change. Strophopteryx nymphs come in two colors: most that we see are yellow and green, but some are brown and orange. In the pre-hatch stage, the wingpads of the yellow/green nymphs get lighter not darker; they look "tan" when the nymph is in water. The wingpads of the brown/orange nymphs, on the other hand, follow the normal pattern we've seen of turning dark brown or black when the insect is ready to hatch.
12/11/10: Buck Mt. Creek. This was the first sighting I had of this genus this season. The nymphs I picked up that day were small, so my photo has to be a microscope shot. Note that the "base" color is yellow: the head, prothorax, and wingpads are "mottled" with olive green and brown spots; the abdomen has alternate stripes of yellow and green. (Strophopteryx nymphs, by the way, almost always "curl up," in this fashion when they're put into alcohol vials -- maybe we would too!)
12/28/10: Buck Mt. Creek. Not the best of photos -- but good enough to make the point. The wingpads are starting to lengthen and the colors are starting to darken.
1/6/11: Buck Mt. Creek.
1/25/11: Buck Mt. Creek. The body is darker with the abdominal stripes -- in this photo at least -- somewhat muted in color. But note how the wingpads are longer and wider than those on the nymphs in the previous pictures.
2/7/11: Buck Mt. Creek. A rare shot of a nymph on a rock. When I turned this rock over, there were 5-6 nymphs moving around. I'm surprised that this shot turned out as well as it did given the low light conditions. Please click on the photo to enlarge to see how the wingpads are changing.
2/14/11: Doyles River. I'd call this nymph fairly mature. The wingpads might get a little bit lighter, but otherwise it's fully developed.
2/14/11: Doyles River. In the same stream, possibly on the same rock (I can't remember), I found the brown/orange version. This was the first time I had seen this color scheme: beautiful! And note that the wingpads are dark.
3/1/11: Buck Mt. Creek. One final shot -- though I'm not sure this is a lot different than the nymph above found on 2/14. I do remember the wingpads on this nymph being "tan": somehow that did not come out as well as I had hoped in the photo.