Butterfly scale form birefringence related to photonics

► Butterfly wing scales have photonic properties that are related to nonlinear optics. ► Form birefringence (BF) was investigated in the wings of two butterfly species. ► BF was found to be related to the constitutive structure of the wings' scales. ► Linear dichroism (LD) at the visible and IR light spectra was detected in the scales. ► BF and LD findings indicate that molecular order characterizes these wings' scales.