Saturday, September 15, 2012

A Very "curious" Heterocloeon curiosum -- and Some Other Nice Finds in the Rivanna River at Crofton

This is a first.  When I saw the color -- the lime green -- of this small minnow mayfly I was sure I had found something new.  Apparently not.  It appears to be a male H. curiosum.  Not what I expected at all.
But it has the forecoxal gills that we find on that species (picture below), the head is the right shape, and it behaved like a male H. curiosum in the tray (they like to stick their heads up towards the top of the water).  And the size is right, ~ 7mm.  Some more photos of this gorgeous nymph.

and with its head popping up...

I'm still bothered by a couple of things with this ID.  One is the color: every male H. curiosum nymph that I've seen looked like this:

They all had the very same dorsal color and pattern.  The other thing that gives me pause -- note the gray pigment in the center in each of the gills in this "regular" H. curiosum:  I see no sign of that in the gills on the nymph from today.   There are other possibilities in the genus of Heteorcloeon -- all with the forecoxal gills: these..

There's H. bernieri which is 7-10 mm long -- but Beaty's team has never seen that in NC.  And there's H. petersi, 7-8 mm long which has "nor dorsal pattern," and on which the "gills [are] grey or grey-brown with [a] light margin" (Beaty, "The Ephemeroptera of North Carolina," p. 9).  But that species is apparently rare and "vulnerable to extirpation."  So, I will stick with H. curiosum for the moment.  But I hope to run this one by Beaty to see if he has a different opinion.

I found two other interesting insects this morning.  One, another Agnetina annulipes common stonefly (the "Southern Stone"), the same species I just found at Buck Mt. Creek.

A real beauty.  On A. annulipes, Beaty notes -- you may recall -- that "sometimes segments 5 and 6 [are] dark mostly to [the] posterior margin."  I think we can see that on this particular nymph; at least the posterior margins of tergites 5 and 6 are clearly darker than those that precede and follow.


One  other treat -- well, if you can call a netspinner a treat!  I found a very colorful common netspinner -- Hydropsyche venularis.  This is the same species I found in the Rivanna at Darden Towe (see the entry posted on 8/4).  But the distinctive head pattern is much clearer on this particular larva.

Remember that the frontoclypeus (top of the head) on this species has two distinct pale spots towards the front that, in some case, merge and form a single stripe.  That's the case here.

I also got a good lateral view.  My photos of the dorsal and lateral aspects of the head on this larva are a good match for the illustrations of H. venularis on p.29 of the "Manual" by Schuster and Etnier.


It was another day when I was initially discouraged with my findings and thinking of going home -- but I ended up finding some beautiful insects.  A lot of the common netspinners I was finding here in the summer, by the way, are gone -- either pupating or hatched.  In their stead, fingernet caddisfly larvae have taken over the grasses that cover the rocks.

No comments:

Post a Comment