Saturday, September 1, 2012

Back to Virginia: Back to Small Minnow Mayflies and Netspinning Caddis

It's not the best time of year to be looking for insects -- aquatic insects -- in central Virginia.  There's not a whole lot to find, nothing new, and what we do find are insects that are not real exciting -- at least from a photographer's point of view.   There are common netspinners, fingernet caddis larvae, baby hellgrammites, though I do find the occasional large one that still hasn't hatched: flatheaded mayflies, genus Maccaffertium, mostly small nymphs, and mostly species that I can't ID; I do see a few common stoneflies (Perlids), but they're still small and lacking in color and pattern.  We can find some cased caddisflies -- strong case-makers (Odontocerids) and humpless case-makers (Brachycentrids), but only when we go to very good streams.     But we do have the small minnow mayflies of summer -- Baetis pluto, Baetis intercalaris, I, and Acentrella nadineae -- many of which are maturing with beautiful colors and patterns.

The A. nadineae small minnow mayfly in the photo at the top of the page is one that I found yesterday in a quick trip to the Doyles River at Blufton Road.  And I was very pleased with the detail that showed up in my pictures.  Note how the gray pigmentation in each of the gills stretches out from the base of the gill to the middle (baso-medial); also note the red/orange markings on the thorax and tergites -- the key features we use in identifying this species.


Of course, I did find a lot of common netspinners (Hydropsychidae), and I looked forward to identifying them to the level of species when I got home.  Unfortunately, I slipped and spilled the bowl I use in collecting, so I was left with only one larva when it was time to take photos.

Still I looked forward to working out another species ID of a genus Hydropsyche larva.  As it turned out this was not a Hydropsyche at all -- it was a genus Cheumatopsyche netspinning larva.  There are two features we use to identify this particular genus: one you cannot see in my photos -- it has a forked fore trochantin -- the other you can.  It does not have a pair of sclerites (dark dots) below the prosternal plate.

As soon as I uploaded this photo I knew what I had.  But this presents us with a new opportunity, yes?
We can work on the species ID of a different genus.  As it turns out, that can't be done.  Beaty tells us to leave this at the level of genus since "almost all Cheumatopsyche larvae are unknown or undescribed."
(Steven Beaty, "The Trichoptera of North Carolina," p. 74.)

Thomas Ames (Caddisflies, pp. 130-133) has some interesting things to say about this netspinner genus, and he confirms one of the things that I've noticed: almost all Cheumatopsyche larvae are bright green in color with a brown head and nota, neither of which has much of a pattern.  (Ames, p. 131) The pale yellow "V" at the front edge of the head on this larva might prove to be species specific, but that remains to be seen.

Ames also notes that Cheumatopsyche is a genus that " transcontinental and occurs in medium to large rivers everywhere south of the tree line.  Peak flight periods in the East are from April through July with continued emergence into October." (Ames, pp. 130-131)  For fly fishermen, this genus hatches as the "Little Sister Caddis."


Even though things are "slow" at the moment in terms of what we can find, I'll continue to go out every week and document what's going on in our streams.  I hope to get back to the Rivanna sometime this week, and when we can be sure of good sunshine -- that may be awhile -- I'll be heading up to the Rapidan River where there are bound to be some surprises.

Additional Note:  I've just learned that in order to distinguish Cheumatopsyche from Hydropsyche larvae, we need to see a medial notch in the frontoclypeal apotome (front edge of the head): Cheumatopsyche larvae have it -- Hydropsyche larvae do not.  The larva in the photo above does indeed have that notch as illustrated in the photo below.

No comments:

Post a Comment