Aquatic Insects of Central Virginia: Mayflies: Pictures of How they Change as they Grow

In the photo above, we see a flatheaded mayfly (genus Epeorus) that is approaching the end of its "aquatic" career, while the spiny crawler (genus Ephemerella) beside it will nearly triple in size in the coming months.

In the photos I've taken in the last 2-3 months, I've been able to capture shots of a couple of mayflies at various stages as they've grown and matured, and in this entry I thought I might put together a kind of "photo history" of the development of the Epeorus flatheaded mayfly. I won't make a lot of comments: the reader can reach his or her own conclusions. I will note the dates on which the photos were taken and the location -- if I can remember! But dates should be understood as no more than guidelines.
Mayfly nymphs grow and develop at different times in different streams -- even in different spots in the same streams. And, they're individuals -- that is to say, when I lift a rock in a stream and see 8-10 flatheads, chances are good there will be babies and toddlers and teens and adults scurrying about all together: they don't all mature and fly off at the same time.

All of those caveats noted -- the most obvious changes you'll see are 1) as they mature, the nymphs become darker, with colors and patterns enriched, and 2) the wingpads get longer and longer and go from being virtually transparent in the beginning to black as they get ready to hatch. I've pointed out the "tips" of the wingpads in each of the photos. (The reader is encouraged to "click" on each photo to enlarge it.)

Flatheaded mayflies: genus Epeorus (probably Epeorus pleuralis), "Quill Gordons" to the fly fishermen.

1. 1/2/11: North Fork of the Moormans. For a microscope photo of an even smaller nymph I collected that day side-by-side with a preserved mature nymph from last year, see the entry for 1/2/11.