Tuesday, October 16, 2012

Finding the "Tubercle" on the netspinner Hydropsyche Betteni

I assure you this is not what I was after today: I went to Mechunk Creek in Cismont in hopes of finding some "baby" Large Winter stoneflies (ours are Taeniopteryx burksi).   Still no luck.  I pretty much saw what I've been seeing everywhere else: brushlegged mayflies and flatheaded mayflies -- lots of them and all very small.

But there was one decent sized common netspinner, so I thought I'd get some photos and see what it was in terms of the species.  Dark head, no pattern: Hydropsyche betteni.  But the neat thing is that in some of the photos I took you can actually see the "tubercle" on the head which Beaty notes in his description.

H. betteni -- larvae 16 mm: has a low rounded tubercle (bump) on back dorsum of head; mature larvae usually have a uniformly dark head while immature larvae may have two light spots or streaks similar to H. venularis.  Widespread.  Most tolerant species.

The tubercle:

Pretty neat.  My friend and I were just lamenting yesterday that on the larvae we've found to date that we thought were H. betteni, we could not see a tubercle at the back of the head.  But, we sure can see it on this one.  And you can make it out on this photo as well.  (Be sure to click on the photos to enlarge them.)

The tolerance value of H. betteni?  7.9.  The EPA Manual on Hydropsyche, by the way, does not mention this tubercle.

The search for large winter nymphs will continue on Thursday.

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