Dead Unique Butterfly

Don't know who stepped on this butterfly.
When I picked up, the lower body is gone, stuck to the floor. But the wings were intact and unique, brown colour and had one near vertical thick line on each wing.
When I dropped the butterfly on a bench, my fingers are littered with brown powder.
When I came back half an hour later, the dead butterfly disappeared. The ants had carried away the body to their nest.