A drifting scrap of white paper can pull a butterfly off course faster than a flower can. In the air, a light rectangle tumbling and flashing at certain angles mimics the key visual cues that many males use to identify potential mates, even though the object is lifeless and flat.
Butterfly eyes contain compound ommatidia tuned to contrast and motion rather than fine detail, and their neural circuits use simple pattern recognition instead of rich image analysis. When a bright, moving patch of the right size crosses the visual field, it can exceed the internal threshold of a signal detection system that evolved under sexual selection: chase first, evaluate later. Wing shimmer, produced by structural coloration and specular reflection, is reduced in the brain to a few parameters like brightness, flicker frequency and trajectory. A tumbling piece of paper can match those parameters closely enough to activate courtship behavior. The same efficiency that allows fast mate location in a cluttered habitat also creates false positives, so a meaningless human artifact is briefly promoted to the status of a possible partner.
A sky full of complex shapes is thus filtered down to crude signals, and in that trimmed‑down world, a scrap of paper can briefly pass for a butterfly.
