Thursday, May 17, 2012

Mystery Insects in Sugar Hollow, I.: The Hellgrammite Nigronia

I'll do this one in two installments since I found two new insects (by genus) today that require identification.  The first, pictured above, is a hellgrammite, genus Nigronia.

The Hellgrammite (dobsonfly) that we normally see is, in terms of the genus, Corydalus, and it looks like this when it's mature:

The family is Corydalidae, on which we find 8 lateral appendages and 2 prolegs at the end, each with a pair of hooks.  It is the gills behind each lateral appendage that makes this Corydalus.

The immature hellgrammite that I found today -- pictured above -- although it has the 4 hooks at the end of its prolegs, is totally lacking in gills.  Here's a microscope photo, ventral view.

So, we leave our "common" hellgrammite behind and move on.  Let me use Peckarksy (Freshwater Macroinvertebrates of Northeastern North America, pp. 174-176) for this one.

If our hellgrammite does not have tufts of gills at the bases of the appendages, we move to the following couplet:

3a.  Last pair of abdominal spiracles (segment 8) at apex of 2 long respiratory tubes extending beyond the prolegs....Chauliodes
3b. Last pair of abdominal spiracles not at apex of long respiratory tubes extending beyond the prolegs....4

The question is -- are there "long respiratory tubes extending beyond the prolegs"?  The "tubes" shoot out between the prolegs -- so the answer is "No".  Nothing extends beyond the prolegs save the appendages on segment 8.  (Look again at the photo above.)

4a.  Each spiracle of 8th abdominal segment at end of short, tapered dorsal respiratory tube, about 1 1/2 times as long as wide; larvae without obvious dorsal pattern on head and thorax....Nigronia
4b. Each spiracle of 8th abdominal segment on posterior edge of segment, not on tube; larvae with distinct dorsal pattern on head and thorax....Neohermes

Our larva is a Nigronia.  1) Note that, while we could argue that there is some kind of pattern on the thorax on our larva, there is certainly no pattern to detect on the head.  And 2) there are "tapered dorsal respiratory tubes" on our larva and they are indeed about 1 1/2 times as long as wide.  I've pointed them out on the following photo.  (A "spiracle," by the way -- and I'm quoting Peckarsky (p. 427) is "the external opening to a tracheal system" -- i.e. it's the opening at the end of the respiratory tube: don't confuse "spiracle" with "appendage.")

And here is a microscope view of those tubes.

The tolerance value for our common hellgrammite -- Corydalus conutus -- is 5.2: the tolerance value for genus Nigronia is undetermined (rarely seen).

The most common insect I found today in this tiny, pristine stream in Sugar Hollow, was our "species unknown" Isoperla Perlodid stonefly that we've seen here before in the spring.  This one.

My bucket was full of them when I stopped to take photos.  This is the Isoperla that entomologists have not identified, and we found it in this stream last year for the very first time.

The stream was full of them.  I imagine they'll be hatching in June.

The "shocker" of the day was this guy (or gal):

Yes, it's a Lepidostomatid case-maker caddis.  Why on earth are they still here in May?!  But if you want to step back in time in terms of the seasons, just go to a high elevation, cold water stream.  We've still got winter insects up here.

Installment II.?  Working out the identification of this Chloroperlid (green stonefly) that I found today.
The genus Sweltsa Chloroperlids that filled these streams in the winter are long gone....or so I assumed.

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