I spotted a fallen leaf... a leaf that is much more than just a fallen aspen leaf.
That made my day! Can you see why?
larvae of the Poplar Petiole Gall Moth (Ectoedemia populella). The galls were home (and food supply) for the caterpillars as they grew during the summer, but now the galls are empty. I found exit holes where the caterpillars left their galls to pupate in the ground.
This photo shows a galled aspen leaf lying on the carpet of leaves underneath the aspen stand.
detail about the aspen galls.