Mayflies: Imago, Subimago

Over the past few days, I've been noticing a large number of mayflies around our apartment. At any given moment now, pretty much every one of our windows has at least one mayfly clinging to the outside -- with all the warm weather we've been having, I guess this is a good time for these little winged insects to emerge from the stream across the street and get busy reproducing.

I've seen mayflies here before, but never so consistently, and so I decided to read up a little on these creatures. As it turns out, they're quite fascinating! I already knew the thing about most adult mayflies living for only 24 hours or less (they spend most of their life as immature larvae underwater), during which time they reproduce, and that's it. But I just now learned that mayflies -- unique among insects -- actually have an immature form that can fly!

After molting from their larval form and emerging from the water, most mayfly species go through what's called a "subimago" stage. They're shaped like adults, and they have functional wings, but they can't yet reproduce. The wings on these subimago mayflies tend to have a dusky, opaque quality, as with this individual I found under my porch light on Monday night:
 

And then, after a short amount of time (a day, or less), the subimago molts into the fully-functioning adult (i.e. "imago"), actually shedding a layer of exoskeleton that covers its entire body, including its wings. I've been finding these shed almost-adult skins on our windows, too, and I brought this one inside to photograph:
 

The covering that was on the mayfly's wings doesn't retain the wing-like shape when the creature molts, apparently, but there are some darker/thicker patches on the empty shell in this picture that I think must be the result of all this material bunching up as the mayfly slips out of its skin.

Now the adult mayfly is ready to go off and do adult things. This adult -- with its crystal-clear wings -- was on our screen door on Sunday (I'm not convinced that it's the same species as the subimago that I photographed above, but still, it's fun to compare the two):

These adults sit on our windows and wave their abdomens from side to side (could they be sensing the air with these motions? I really have no idea), and as a result, they've gained the fond nickname of "butt-wigglers" in our home.

Who knew that such inconspicuous animals could be so interesting? Insects can be pretty darn cool!