The Hercules Beetle is remarkable, not only for its strength, able to carry up to 850 times its own weight, the protective outgrowth of the insects’ exoskeleton, also changes from green to black as its surrounding atmosphere gets more humid.Researchers from the University of Namur in Belgium have used the latest imaging techniques to study the shell of the beetle - a scanning electronic microscope to determine the structure responsible for the colour and a spectrophotometer to analyze how the light interacts with this structure.
The light interferes with the structure to produce the green colour of the shell. When water penetrates through the widely-open porous layers, it destroys the interferences phenomenon leading to a black colouration.
As to why the beetle changes colour, question marks also remain. Some have suggested that it is to do with protection – it becomes more humid at night and is therefore good for cover to turn black. Others have suggested that it is to do with warmth absorption at night. Questions remain.
Marie Rassart, who did the research at the University of Namur, said, “The sort of structural behaviour displayed by the Hercules Beetle could be an important property for ‘intelligent’ materials’. Such materials could be put to work as humidity sensors. This could be useful for example in food processing plants to monitor the moisture level.” link
Diffractive hygrochromic effect in the cuticle of the hercules beetle Dynastes Hercules. 2008. M Rassart et al 2008 New Journal of Physics: (14pp).