Do Mayflies live long enough to shed an exoskeleton?

Male subimago exuvia

The size estimate surely includes the tails, which makes it harder to interpret. The candidates for a relatively large early-season dark mayfly in your area would likely be Epeorus pleuralis, Ephemerella subvaria, or one of the Leptophlebia species. E. pleuralis has two tails. The middle caudal filament of Leptophlebia is thinner and shorter than the cerci. It is really hard to tell whether that might be the case in this photo, but I do tend to lean toward a Leptophlebiidae ID. If I could see the claspers close up, it would be easy to distinguish between Leptophlebia and Ephemerella. However, if the body length of the exuvia was more in the 7-8mm range, Paraleptophlebia would make sense.

… Lloyd Gonzales, 13 November, 2008 - 12:26pm

Don't know, but...

When I was a kid in Ohio, a hatch would cover the side of our garage. Live one day, then "husks" like yours the next.

… Ron Hemberger, 30 April, 2007 - 8:59am

Old skin

Mayflies emerge from their aquatic home as subimagos (see another comment that I just made). They then shed their skins one last time to become adults that are able to reproduce. Look closely at the thorax of this exoskeleton and you will see the remains of the wings.
Often, subimagos will mass-emerge and molt simultaneously, then fly away to mate, lay eggs and ultimately die in the water body from which they emerged. This is the phenomenon which Ron observed.

… Stephen Luk, 30 April, 2007 - 11:49am