Mayfly - in May

I spotted something fluttering about on my car, (don't worry, it was stationary on our drive at the time, and I was in the house) so went to have a look. It was two mayflies, one on the rear wiper, and one on the roof. 
The one on the wiper looked as though he was struggling a bit, and it also looked as though another had died on the wiper.
A quick trip to Google has revealed all. Evidently the mayfly eggs develop into nymphs, which may spend up to 2 years on the bottom of the river or stream. The mayfly nymph then emerges from the water as a mayfly, but is rather dull-looking "sub-imago" (which I think is the equivalent of being a mayfly goth teenager) and looks for somewhere to hide, normally in the vegetation on the river bank. A few hours later the sub-imago will shed its skin once more,  and will now be a brightly coloured "imago" (or grown-up).   
I think that this is what I saw happening on my car - the one was struggling to get out of his skin on my rear wiper! That makes sense really, as the river is only about 100 metres away, and they must have mistaken my dirty car for vegetation. 
I've put an extra pic in of the one struggling on the wiper.