A SOUTH American butterfly is the first animal known to use polarised light to find mates.
Alison Sweeney at Duke University in Durham, North Carolina, and a team tested whether captive male Heliconius butterflies are attracted to polarised light reflected off the wings of females.
Males paid significantly more attention to females when they could see a polarised signal (Nature, vol 423, p 31).
Sweeney speculates that polarised light helps males to pick out potential mates obscured by forest undergrowth. “The signal will always be there no matter what colour of light it is reflecting,” she says.
