It's the underside of a piece of rotting bark my kids peeled off a tree!
The boys were fascinated by the paths and impressions that the little creatures left behind on the underside of this piece of bark. They stared at it then ran off to gather all they could find to display in their tree house.
Wouldn't it be lovely framed? I might let it dry then brush on a finish to bring out the colors and mount it in a shadowbox...maybe after a good spray with Seven insecticide though.