The Hercules beetle native to South America has a fascinating trait of changing its shell colors depending on the external humidity conditions. This is because the inside of the beetle's shell consists of porous lattice structure with square holes. When light of particular wavelengths hits the shell, it reflects them and displays different colors; and these wavelengths change depending on the humidity. Recently, a sensor that changes colors depending on the humidity like this beetle with 10,000 times faster speed than the conventional optical sensors has been proposed.