Neutron scattering and in particular SESANS is able to give us excellent ensemble averaging of the optical properties of materials which exhibit structural colour. We plan to use SESANS to measure the volume fraction of chitin and air in ultra white beetle scales and give an effective g(r). We also want to use SESANS to measure the ridge architecture and optical nanostructure of a carefully selected subset of the south american heliconius butterflies. Here we have genetic information about these individuals and we would like to use the powerful averaging power of neutrons to probe what look essentially like grating structure. Larmor is highly sensitive to such structures and able to collect excellent data. Comparisons of these butterflies will help us to pinpoint DNA sequences that may be responsible for controlling the development and structuring of butterfly optical structure.