Thursday, December 16, 2010

Large Winter Stoneflies (genus Taeniopteryx)

Stream monitors tend to sample streams very little during the winter -- if at all.  It's not very pleasant, of course, sloshing through near freezing water and sitting in snow banks and counting bugs!  Nonetheless, there is a lot to see in our streams from November through February, things that many monitors miss.  Many mayflies, for example, make their appearance as very small nymphs in late November and/or December -- e.g. small minnow mayflies and spiny crawlers -- and they get bigger and bigger as the winter proceeds.

Another thing that is commonly missed is the chance to see the beautiful large winter stoneflies (we have two genera in our streams, Taeniopteryx and Strophopteryx, this article will only deal with the first).  Taeniopteryx nymphs appear in our streams around mid-October, reaching maturity in January and February when they hatch into their terrestrial form.  The top photo above shows a mature nymph from a stream in January this year: below it is a tiny nymph (actual length, 1/8") that we found on October 24.  When mature, these nymphs are easy to spot -- dark brown in color with a light stripe that runs from the thorax to the end of the abdomen.  But the "defining features" of a Taeniopteryx nymph are the "coxal gills":  long, clear, finger-like projections that stick out from the base of each leg. (second photo above -- very enlarged).

Large winter stoneflies molt numerous times as they mature.  The photo below shows a Taeniopteryx nymph found in late November -- a "teenager," if you will.  If you look closely, you can see the "coxal" gills in clear view behind each of the legs.

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