A tale of two stoneflies
I suppose I could title this post A winter’s tale. Or perhaps Winters’ tails.
There are two stoneflies that make their appearance in Massachusetts in the winter and early spring, both of which bespeak of winter in their common name. The small winter stonefly, (a.k.a. snowfly, family Capniidae), has been seen by River’s Calendar members as early as February 10 in this and in past years. The ones we’ve seen range in size from 4-6 millimeter, or approximate hook sizes #18 – 22. The females appear to be larger than the males. Males can have rather short wings, some not quite extending to the end of their abdomens. Capniidae are quite thin, body and wing.
The winter stonefly (a.k.a. willow fly or early brown stonefly, family Taeniopterygidae) may emerge a little later than Capniidae – we’ve seen them March into April. These run a little larger; 6-7 millimeters, or size #16-18.
In trying to tell these two apart, time of year and size can help, but there is some overlap in both. A close look at tails and wings can help.
If you see tails extending well beyond the wing, it’s likely a Capniidae.
At least some of the Taenipterygidae have wings that are slightly club shaped, like a bowling pin; they get wider towards the tail end. But a better diagnostic cue is the pattern on the wings. Taenipterygidae have two rows of veins that are more or less parallel, with cross veins that look like rungs on a ladder. These are seen close to the base of the wings. The wings on Capniidae don’t exhibit this pattern. They veins are less neatly organized.
Here’s a photo that illustrates these properties - tails, shape and pattern of the wings. Taeniopterygidae on top, Capniidae on the bottom. Note these are not to scale. The Capniidae was the smaller of the two specimens.
https://www.flickr.com/photos/79718069@N00/13903371796/
I had thought that neither of these stoneflies seem to be important to fish, at least not in their adult form. The high and cold water conditions generally found at this time of year aren't conducive to rising trout. However, as Dan mentions in a comment below, fish will rise to them under some conditions. Dan, were the stoneflies in the trout stomach adults? Has anyone else had experience of fish rising to these flies?
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For the last 40 years, the 1 st week of march I can catch native brook trout on top using black stone fly imitations in the Quaboag River, Warren, MA. There is usually snow on the banks but the river is low as the snow melt is just starting. The Swift River is different , the water being colder; there is very little surface activity.
However on 4-17-2014, I pumped a trout on the Swift River and among several other organisms were 14 Capniidae. Water temp was 41.1 F.
Thanks for the info, Dan. Just yesterday, I saw several winter stoneflies (Taeniopterygidae) on the West Branch of the Swift, in Shutesbury. The water was clear, probably a bit high but not unusually so. No snow on the banks. Some of the stoneflies were running across the water, wings fluttering, to reach the shore. I didn't see any fish, but I can see how this type of action might attract their interest and appetites.
A friend, doing some early May small stream fishing in Central Mass, showed me contents of a trout's stomach that he'd pumped. He found several adult stoneflies; Capniidae as well as Taeniopterygidae.
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