On a Nannyberry shrub. It is a tiny (4 mm?) treehopper. The thorny projection is actually an outgrowth of the pronotum that serves as a sort of shield over its body. They are common insects but extraordinarily hard to see because they are so small and look so much like part of a twig, like a leaf bud for example. Although this one is walking along the twig (heading to the right...the head is under the "thorn"), when they are sitting still they are nearly invisible. I looked for nearly an hour today on a shrub where I know they occur but in the end saw only three.