An Electron Microscope Study of Some Structural Colors of Insects

The electron microscope has been used to study two types of structures responsible for the physical colors of insects. The iridescence of the beetle Serica sericea is due to a line grating on its wing-covers, 0.8μ between lines. The structure giving rise to the brilliant blue color of the tropical butterfly Morpho cypris is quite elaborate, consisting essentially of hundreds of vanes on each wing scale, the vanes possessing linear thickenings 0.2μ apart which reinforce the reflection of blue light. Numerous exceedingly fine markings on parts of the wing scales go down in dimensions to 60A, and some of them may be related to the chemical structure of the scales. Chemical tests show that the scales are not composed of chitin, the principal component of the external parts of most insects. It is interesting that bombardment of the scales with an intense electron beam (1000 electrons per square angstrom per second) for a matter of minutes does not appreciably affect the swelling properties of the scales in organic liquids.