I've been seeing these strange creatures on our little cabin. They look a bit like a cross between a cicada shell and a spider. All of them are hollow (as in not alive) and have an opening on their backs. Finally, finally, the mystery was revealed! They are the remains of dragonfly nymphs. Here are some photos of one "hatching" this morning. The process is truly amazing.
And here are two other dragonflies, in various stages of their transformations: