The researchers found that some dragonflies exhibit ultraviolet light (UV) reflectance and water repellency using wax with a unique composition that differs from previously-known organismal waxes, in collaboration with Hamamatsu University School of Medicine, Nagoya Institute of Technology, and Tokyo University of Agriculture.

Change in body color and light reflectance during adult maturation of the dragonfly Orthetrum albistylum (solid line: dorsal side; dashed line: ventral side)

Animals and plants reflect UV on their body surface, which seems to be important for protection against UV-induced damages. Research on the UV reflection of living organisms has been mainly focused on the description of surface microstructures, whereas the chemical composition of UV reflective materials and the genes involved in the production of these materials have been poorly understood. Adult males of the white-tailed skimmer dragonfly (Orthetrum albistylum) are known to be coated with a wax that reflects UV light, but the composition of this wax has been unknown.

Measurements of the light reflectance of the body surface of O. albistylum showed that, as adult males mature and secrete wax, the reflectance of short-wavelength light increases mainly on the dorsal side. Chemical analysis of the dragonfly wax revealed that three very long-chain methyl ketones and four very long-chain aldehydes are the major components, which totally differ from previously-known organismal waxes. Chemical synthesis and recrystallization of a very long-chain methyl ketone resulted in the formation of a microstructure with strong UV reflection and water repellency, which are similarly found on the wax-coated body surface of UV reflective dragonflies.

The researchers will investigate the characteristics of the UV reflective wax of O. albistylum in more detail, including stability and antibacterial properties.