Thursday, May 16, 2013

Let's give the Spiny Crawlers their due

This morning I went to a small mountain stream in Sugar Hollow, one of the seven that I visit in a fairly regular way.  I saw quite a few Perlodid stoneflies -- Isoperla holochlora, Remenus bilobatus, and that unknown Isoperla on which I focussed last week (5/10).  But the leaf packs were loaded with spiny crawler mayflies -- Ephemerella dorothea from what I could see -- which is true of leaf packs in just about all of our streams at the moment.

It's their time of year.  This may be the single most prolific insect we find in our streams, and they show up in April and May.   When I monitored streams, I remember being disappointed when samples were dominated by spiny crawlers.  That had a negative impact on the "score" of the stream.  In Virginia, to begin with (unless things have changed), all spiny crawlers -- every genus and species -- are given a tolerance value of 4 (scale of 1 to 10), and whenever one insect family accounts for, say, two thirds of the sample, the stream is seen to be lacking in the variety that's always desired (which also brings down the score.  Also, I never found them very attractive.

Point one: scores are bound to be skewed if every genus and species of a particular insect are given the same tolerance value.  Most of the spinys that we see at the moment are E. dorothea with a TV (in North Carolina) of 3.3, but we also see E. invaria (TV, 2.6), Drunella tuberculata (TV, 0.0), and Drunella walkeri (TV, 0.6).

Point two:  at this time of year, we are bound to get samples that are dominated by spinys -- it's inevitable.   And the lack of variety in our samples does not indicate that we're dealing with so-so streams.   The stream that I went to this morning was a head-water stream, a first order stream, one that is filled with quality insects.  Still, this morning, spiny crawlers probably accounted for 75% of the insects I saw.

And point three: if you think that spiny crawlers are "ugly," you're not looking at them very closely (which is true if you're just picking them off of a net).  Look at that beauty at the top of the page.  And here are more photos that I took this morning, all E. dorothea, three nymphs that differed in color and pattern.

Tis the season folks: take a close look and enjoy!

Just one other photo -- a very nice Isoperla holochlora.  They too are very numerous at the moment in these small mountain streams.  Tolerance value: 0.7.

No comments:

Post a Comment