Saturday, February 19, 2011

Large Winter Stoneflies and Using Voshell

Since I mentioned J. Reese Voshell's seminal work -- A Guide to Common Freshwater Invertebrates of North America -- in my previous entry, I think that two more comments ought to be made.

1) This is clearly a book that should have been on my "simply must have" list of works needed by amateur entomologists and stream monitors everywhere (see "The Amateur Entomologist's Bibliography, 2/11/11).   Omitting this was an oversight.

2) The illustration that he provides on p. 134 (Plate 47) of a large winter stonefly essentially matches the photo above -- it's genus Taeniopteryx.   Confirming that, he says, "The most common kinds [of large winter stoneflies] in the East have a single, finger-like, segmented gill on the first leg segment closest to the body." (I.e. they have "coxal gills.")

For people who do winter sampling, I think this can be very misleading.  True, we see a lot of this genus in early winter, but in February and March, we see few if any at all.  Almost all large winter stones that we see at the moment are genus Strophopteryx (photo below).

And my own feeling is that, if we look at the season for large winter stones overall, in our watershed we see more Strophopteryx large winter stoneflies than Taeniopteryx large winter stoneflies.  Using only Voshell, I don't think someone sampling a stream would conclude that the nymph in the picture above was a large winter stonefly (and he/she sure wouldn't find "coxal gills").

This is one place where I think both genera should have been pictured and discussed.

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