I borrowed this specimen from school's biology class. This is tropical butterfly Caligo oileus (Brown Owl butterfly, or Oileus Giant Owl). This fragment is the part of white rim around big "eye" at rear side of the wings.
Gear: my usual "snowflake" macro setup (i described it in article about snowflake macro photography). Daylight from top, no diffusors, no reflectors. Averaged 64 RAWs, no focus stacking.
Fragment in original resolution: