The last leaf on a tree may hold a treasure...

... if your definition of "treasure" includes a cocoon or a chrysalis of a moth or butterfly.  I was walking in a park several weeks ago, prior to the spring leaf-out, and noticed the above rather anomalous appearance of an aspen twig, which had a dead leaf still attached.  Some trees (notably oaks) exhibit marcescence, but not aspens, so I took a closer look.

Here is the same twig/leaf viewed from the other side...

... and you can see the cocoon nestled in to its well-disguised hidey-hole.  I brought it home and put it out on the screen porch hoping to see the inhabitant eclose this spring, but I don't have very high hopes because I think that small gap in the silk at the top represents the site of emergence of a parasitic wasp.  Butterflies and moths are primary prey for a variety of wasps, both while caterpillars and while in their pupae.  I think a wasp found this cocoon before I did. 

Click to enlarge the photos.  Can anyone offer an suggestion re the species?