It was bound to happen. If you go to streams as often as I do, putting mayfly nymphs and stonefly nymphs -- some fully mature -- into your bowl, someday, something is going to hatch. And it happened today, and I got to see it step-by-step.
Here's the nymph I had collected.
The colors looked a little bit off -- A. nadineae nymphs are very distinct with splotches of red and orange. E.g. here's a a real beauty that I photographed on 8/30/12.
Still, there was no doubt about the ID. Look at the gills. From Beaty, "gills elongate, asymmetrical, and with basomedial pigmentation splotches." ("The Ephemeroptera of North Carolina," p. 4) No doubt about it.
Before very long, I had two signs that this nymph was in the process of hatching. In this photo -- in which the nymph is "hitching a ride" on a "Weighted case-maker" (Goeridae) -- note how the tails are curling up. That's what they look like on the adults. In fact, this looks like an adult sans the wings.
Second sign. Note the "bubble" that has appeared on the thorax of the nymph. The thorax is cracking as the wings start to emerge.
In a flash, the wings came out and the adult popped out of my dish. (Shoot! Forgot to look in my dish for the "shuck.")
But before it flew away -- and it did -- it perched on my petri dish long enough for me to get a couple of photos.
That was a treat. If I use some of the photos I have in my files, we can see the whole process of maturation.
1) tiny nymph
2) a nymph that's fairly mature
3) fully mature -- black wing pads
and then from today ---
And for the fly fishermen in the group -- time to get out the BWO's (Blue-winged Olives). The fall hatch has begun.
A few other photos from this morning -- though not nearly so exciting.
1. Small minnow mayfly, Baetis intercalaris. Also fairly mature.
2. A pair of Goera calcarata "Weighted case-makers."
3. And the smallest of the small: spiny crawler mayfly, Ephemerella subvaria. Recognized it by the colors. We see the large, mature nymphs in March and April.
For a complete description of the hatching/emerging process, see Knopp and Cormier, Mayflies: An Angler's Study of Trout Water Ephemeroptera, pp. 10-16.