Thursday, May 19, 2011

So many species -- so little time! Perlodid Isoperlas

It was a frustating day on the stream: in one sense, a disaster!   But more on that in a moment.

We had 3.5 inches of rain on Tuesday -- another 1/2 inch yesterday.    Where on earth did I find any clean water to search for some bugs?  I decided to look at one of the tribs to the Moormans I sample -- one that goes unnamed.  The water was high and roaring -- but clear -- so I assembled my gear and started to look.

Nothing under the rocks (well, one lonely Epeorus flatheaded mayfly): the water was simply too swift.
So I started sorting through leaf packs.  That proved to be very productive.  They were loaded with spiny crawlers -- no surprise there -- and I picked up all sorts of stoneflies.  I even found a Dytiscid (a Predaceous Diving Beetle: photos to follow below).  But the "prize" was a BIG common burrower mayfly -- over an inch in length -- that I think was genus Hexagenia.  I have to say "I think" because I never got a picture (= disaster)!   When I went to put it into my dish for a photo, I dropped it, and although I looked myself silly, I never found it.  What a loss!  I hope this isn't a "once in a lifetime".  Common burrowers (Ephemeridae) live in the substrate, but this one had clearly been washed into the leaves by the scouring of the stream.

The other problem I had -- well, it's not really a problem -- was that I found all sorts of Perlodid stoneflies that I knew were Isoperlas (confirmed at home with the microscope) -- but they're species that I don't recognize, with the exception of one holochlora.  Pictures.

1) Another shot of the one in the photo above.  First time I've seen this species.

2) Isoperla type two

and 3) a pair of Isoperlas -- the one on the left is Isoperla holochlora.

So many species -- so little time.  (Stewart and Stark -- Nymphs of North American Stonefly Genera, pp. 412-13 -- list a total of 57 species of Isoperla in North America, but only 11 are attested for Virginia.)

Just a couple of other photos to show.  One is a beautiful spiny crawler (genus Ephemerella): they're really starting to mature.

Another: an adult Perlodid stonefly.  I suspect it's genus Isoperla.

And finally, a couple of pix of the Dytiscid (predaceous diving beetle).  The first is a live shot: the second, one done at home with my microscope.  Anyway you look at it, this is one mean looking critter!  In the microscope photo, it's easy to see the "breathing tube" this insect uses as a "snorkel" to get its air.  (Click on the photo to enlarge.

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