The Rapidan River is chock-a-block full of nymphs at the moment, as it always is in the spring. And this is one of the stoneflies I was hoping to find: Perlodidae, Isogenoides hansoni. This is still the only place that I've found these beautiful nymphs, and as I suspected, they're pretty close to being mature. Still, not yet quite as mature as the nymph that I found on 3/24/11.
I think I'll just focus on photos today, with minimal comments on features we use for ID. For I. hansoni, the banding on the abdominal terga is clearly distinct, but I always look at the head: "ocellar triangle bordered by dark but with pale central spot." (Beaty, "The Plecoptera of North Carolina," p. 22)
There you go.
Another treasure today -- an Agnetina capitata (Perlidae) that still has a ways to go before it's mature.
Another species that, to date, I've only found in this river. Agnetina common stones have a setal row on the occiput and very clear anal gills. A. capitata has a light area between the lateral ocelli that leads towards the median ocellus and an "apparent" mid-dorsal longitudinal stripe on the terga. (Beaty, "The Plecoptera of North Carolina," p. 15)
These nymphs will mature in late May and June. Found this one last year on 5/24.
But today, those wing pads were just starting to curve.
And then there was this HUGE Giant stonefly, Pteronarcys biloba.
That big boy would make a real meal for the native Brookies that live in this stream. It ran about 2 inches. But it was so active, and so big, that it kept crawling out of my petri dish. I had to retrieve it a number of times.
Mayflies? Of course. I only photographed two, two that were very mature. The spiny crawler, Ephemerella subvaria,
and the small minnow mayfly that we find only in clean mountain streams, Baetis tricaudatus.
The short middle tail (caudal filament) is very clear in both of those photos.
It's a special river, and these are all special insects.
1. Isogenoides hansoni: "Relatively rare" according to Beaty (p. 22).
2. Agnetina capitata: "Listed by NC Natural Heritage Program as Significantly Rare (2010)." (Beaty, p. 15)
3. Pteronarcys biloba: tolerance value of 0.0.
4. Ephemerella subvaria: "Rare," according to Beaty. ("The Ephemeroptera of North Carolina," p. 28)
5. and Baetis tricaudatus: tolerance value of 1.5.
Off to Buck Mt. Creek on Tuesday where we should find a fair number of Isoperlas (Perlodid stoneflies), and then to the small mountain streams in Sugar Hollow next weekend.
Most common insect today: Perlodid stonefly, Isoperla montana/kirchneri. The leaf packs are crawling with them at the moment. I'd look for the "Yellow Sallies" to hatch sometime in late April.