I went to Long Island Creek (Fluvanna County) today to see if the "Prong-gilled" Mayfly (family: Leptophlebiidae) nymphs were around -- and sure enough they were! Long Island Creek is a small stream to the east of Palmyra, and it tends to have very good bugs; i.e. it's healthy water. I found a rich assortment of insects today without looking real hard. The insects were mostly in leaf packs, of which there were many, most of them pretty thick. The inventory for the day reads as follows: lots of small winter stoneflies and lots of large winter stoneflies (very colorful, very mature); a few Perlodid stoneflies (genus to be determined); a fair number of fairly large Common stoneflies (Perlids: all genus Eccoptura), a nymph I've seen only rarely in recent weeks. I also found mayflies: in addition to a handful of Prong-gilleds, there were quite a few Flatheaded mayflies (genus Stenonema/Maccafertium), some of them large, and I found one Brushlegged mayfly. In the Caddis department, I found a few Fingernet caddisflies, one Netspinner (genus Diplectrona), and a bunch of Uenoid casemakers sticking to rocks.
The Prong-gilled mayfly is one that hatches early on in the spring (March-May), so we often see nymphs in the winter, but it hatches again (different species) in the fall (July-October), so we see them again in the summer. The adult, terrestrial is known to fly fishermen as the "Blue Quill". It is an insect we find in very few of our streams. It is intolerant of stream impairment (TV of 1.2 in the southeast), and is only found, therefore, in clean, rocky, small streams. Interestingly, most of the streams where we find them in significant numbers are in Fluvanna County: Long Island Creek, Raccoon Creek, and the stream used by StreamWatch as its reference site in Fluvanna County. In Albemarle County, you'd best go to the Doyles River where it flows out of the Park if you want to see them. The following photo of a live Prong-gilled mayfly was taken at the Rapidan River.
In this mayfly family, genus determination is based largely on the shape of the gills. All of our Prong-gilled mayflies appear to be genus Paraleptophlebia. It is rare to get a photo like the photo below: when these nymphs are preserved, their gills are easily broken off.